diff --git a/tests/Executor/AbstractPromiseTest.php b/tests/Executor/AbstractPromiseTest.php
index 0ea9a4f..8a6f1d1 100644
--- a/tests/Executor/AbstractPromiseTest.php
+++ b/tests/Executor/AbstractPromiseTest.php
@@ -21,7 +21,7 @@ class AbstractPromiseTest extends TestCase
     /**
      * @see it('isTypeOf used to resolve runtime type for Interface')
      */
-    public function testIsTypeOfUsedToResolveRuntimeTypeForInterface()
+    public function testIsTypeOfUsedToResolveRuntimeTypeForInterface() : void
     {
         $PetType = new InterfaceType([
             'name' => 'Pet',
@@ -105,7 +105,7 @@ class AbstractPromiseTest extends TestCase
     /**
      * @see it('isTypeOf can be rejected')
      */
-    public function testIsTypeOfCanBeRejected()
+    public function testIsTypeOfCanBeRejected() : void
     {
 
         $PetType = new InterfaceType([
@@ -199,7 +199,7 @@ class AbstractPromiseTest extends TestCase
     /**
      * @see it('isTypeOf used to resolve runtime type for Union')
      */
-    public function testIsTypeOfUsedToResolveRuntimeTypeForUnion()
+    public function testIsTypeOfUsedToResolveRuntimeTypeForUnion() : void
     {
 
         $DogType = new ObjectType([
@@ -277,7 +277,7 @@ class AbstractPromiseTest extends TestCase
     /**
      * @see it('resolveType on Interface yields useful error')
      */
-    public function testResolveTypeOnInterfaceYieldsUsefulError()
+    public function testResolveTypeOnInterfaceYieldsUsefulError() : void
     {
         $PetType = new InterfaceType([
             'name' => 'Pet',
@@ -383,7 +383,7 @@ class AbstractPromiseTest extends TestCase
     /**
      * @see it('resolveType on Union yields useful error')
      */
-    public function testResolveTypeOnUnionYieldsUsefulError()
+    public function testResolveTypeOnUnionYieldsUsefulError() : void
     {
 
         $HumanType = new ObjectType([
@@ -484,7 +484,7 @@ class AbstractPromiseTest extends TestCase
     /**
      * @see it('resolveType allows resolving with type name')
      */
-    public function testResolveTypeAllowsResolvingWithTypeName()
+    public function testResolveTypeAllowsResolvingWithTypeName() : void
     {
         $PetType = new InterfaceType([
             'name' => 'Pet',
@@ -569,7 +569,7 @@ class AbstractPromiseTest extends TestCase
     /**
      * @see it('resolveType can be caught')
      */
-    public function testResolveTypeCanBeCaught()
+    public function testResolveTypeCanBeCaught() : void
     {
 
         $PetType = new InterfaceType([
diff --git a/tests/Executor/AbstractTest.php b/tests/Executor/AbstractTest.php
index f6eda0a..38ebd1f 100644
--- a/tests/Executor/AbstractTest.php
+++ b/tests/Executor/AbstractTest.php
@@ -21,7 +21,7 @@ class AbstractTest extends TestCase
     /**
      * @see it('isTypeOf used to resolve runtime type for Interface')
      */
-    public function testIsTypeOfUsedToResolveRuntimeTypeForInterface()
+    public function testIsTypeOfUsedToResolveRuntimeTypeForInterface() : void
     {
         // isTypeOf used to resolve runtime type for Interface
         $petType = new InterfaceType([
@@ -95,7 +95,7 @@ class AbstractTest extends TestCase
     /**
      * @see it('isTypeOf used to resolve runtime type for Union')
      */
-    public function testIsTypeOfUsedToResolveRuntimeTypeForUnion()
+    public function testIsTypeOfUsedToResolveRuntimeTypeForUnion() : void
     {
         $dogType = new ObjectType([
             'name' => 'Dog',
@@ -265,7 +265,7 @@ class AbstractTest extends TestCase
     /**
      * @see it('resolveType on Union yields useful error')
      */
-    public function testResolveTypeOnUnionYieldsUsefulError()
+    public function testResolveTypeOnUnionYieldsUsefulError() : void
     {
         $HumanType = new ObjectType([
             'name' => 'Human',
@@ -360,7 +360,7 @@ class AbstractTest extends TestCase
     /**
      * @see it('returning invalid value from resolveType yields useful error')
      */
-    public function testReturningInvalidValueFromResolveTypeYieldsUsefulError()
+    public function testReturningInvalidValueFromResolveTypeYieldsUsefulError() : void
     {
         $fooInterface = new InterfaceType([
             'name' => 'FooInterface',
@@ -415,7 +415,7 @@ class AbstractTest extends TestCase
     /**
      * @see it('resolveType allows resolving with type name')
      */
-    public function testResolveTypeAllowsResolvingWithTypeName()
+    public function testResolveTypeAllowsResolvingWithTypeName() : void
     {
         $PetType = new InterfaceType([
             'name' => 'Pet',
@@ -489,7 +489,7 @@ class AbstractTest extends TestCase
         ], $result);
     }
 
-    public function testHintsOnConflictingTypeInstancesInResolveType()
+    public function testHintsOnConflictingTypeInstancesInResolveType() : void
     {
         $createTest = function() use (&$iface) {
             return new ObjectType([
diff --git a/tests/Executor/DeferredFieldsTest.php b/tests/Executor/DeferredFieldsTest.php
index 083d24c..775b5ab 100644
--- a/tests/Executor/DeferredFieldsTest.php
+++ b/tests/Executor/DeferredFieldsTest.php
@@ -180,7 +180,7 @@ class DeferredFieldsTest extends TestCase
         parent::setUp();
     }
 
-    public function testDeferredFields()
+    public function testDeferredFields() : void
     {
         $query = Parser::parse('
             {
@@ -272,7 +272,7 @@ class DeferredFieldsTest extends TestCase
         $this->assertEquals($expectedPath, $this->path);
     }
 
-    public function testNestedDeferredFields()
+    public function testNestedDeferredFields() : void
     {
         $query = Parser::parse('
             {
@@ -349,7 +349,7 @@ class DeferredFieldsTest extends TestCase
         $this->assertEquals($expectedPath, $this->path);
     }
 
-    public function testComplexRecursiveDeferredFields()
+    public function testComplexRecursiveDeferredFields() : void
     {
         $complexType = new ObjectType([
             'name' => 'ComplexType',
diff --git a/tests/Executor/DirectivesTest.php b/tests/Executor/DirectivesTest.php
index 3b22e21..295e2f1 100644
--- a/tests/Executor/DirectivesTest.php
+++ b/tests/Executor/DirectivesTest.php
@@ -13,18 +13,14 @@ class DirectivesTest extends TestCase
     // Describe: Execute: handles directives
 
     /**
-     * @describe works without directives
      * @see it('basic query works')
      */
-    public function testWorksWithoutDirectives()
+    public function testWorksWithoutDirectives() : void
     {
         $this->assertEquals(['data' => ['a' => 'a', 'b' => 'b']], $this->executeTestQuery('{ a, b }'));
     }
 
-    /**
-     * @describe works on scalars
-     */
-    public function testWorksOnScalars()
+    public function testWorksOnScalars() : void
     {
         // if true includes scalar
         $this->assertEquals(['data' => ['a' => 'a', 'b' => 'b']], $this->executeTestQuery('{ a, b @include(if: true) }'));
@@ -39,10 +35,7 @@ class DirectivesTest extends TestCase
         $this->assertEquals(['data' => ['a' => 'a']], $this->executeTestQuery('{ a, b @skip(if: true) }'));
     }
 
-    /**
-     * @describe works on fragment spreads
-     */
-    public function testWorksOnFragmentSpreads()
+    public function testWorksOnFragmentSpreads() : void
     {
         // if false omits fragment spread
         $q = '
@@ -93,10 +86,7 @@ class DirectivesTest extends TestCase
         $this->assertEquals(['data' => ['a' => 'a']], $this->executeTestQuery($q));
     }
 
-    /**
-     * @describe works on inline fragment
-     */
-    public function testWorksOnInlineFragment()
+    public function testWorksOnInlineFragment() : void
     {
         // if false omits inline fragment
         $q = '
@@ -143,10 +133,7 @@ class DirectivesTest extends TestCase
         $this->assertEquals(['data' => ['a' => 'a']], $this->executeTestQuery($q));
     }
 
-    /**
-     * @describe works on anonymous inline fragment
-     */
-    public function testWorksOnAnonymousInlineFragment()
+    public function testWorksOnAnonymousInlineFragment() : void
     {
         // if false omits anonymous inline fragment
         $q = '
@@ -193,10 +180,7 @@ class DirectivesTest extends TestCase
         $this->assertEquals(['data' => ['a' => 'a']], $this->executeTestQuery($q));
     }
 
-    /**
-     * @describe works with skip and include directives
-     */
-    public function testWorksWithSkipAndIncludeDirectives()
+    public function testWorksWithSkipAndIncludeDirectives() : void
     {
         // include and no skip
         $this->assertEquals(
@@ -217,9 +201,6 @@ class DirectivesTest extends TestCase
         );
     }
 
-
-
-
     private static $schema;
 
     private static $data;
diff --git a/tests/Executor/ExecutionResultTest.php b/tests/Executor/ExecutionResultTest.php
index deab57a..69fbd78 100644
--- a/tests/Executor/ExecutionResultTest.php
+++ b/tests/Executor/ExecutionResultTest.php
@@ -6,14 +6,14 @@ use PHPUnit\Framework\TestCase;
 
 class ExecutionResultTest extends TestCase
 {
-    public function testToArrayWithoutExtensions()
+    public function testToArrayWithoutExtensions() : void
     {
         $executionResult = new ExecutionResult();
 
         $this->assertEquals([], $executionResult->toArray());
     }
 
-    public function testToArrayExtensions()
+    public function testToArrayExtensions() : void
     {
         $executionResult = new ExecutionResult(null, [], ['foo' => 'bar']);
 
diff --git a/tests/Executor/ExecutorLazySchemaTest.php b/tests/Executor/ExecutorLazySchemaTest.php
index a62091c..d388735 100644
--- a/tests/Executor/ExecutorLazySchemaTest.php
+++ b/tests/Executor/ExecutorLazySchemaTest.php
@@ -41,7 +41,7 @@ class ExecutorLazySchemaTest extends TestCase
 
     public $loadedTypes = [];
 
-    public function testWarnsAboutSlowIsTypeOfForLazySchema()
+    public function testWarnsAboutSlowIsTypeOfForLazySchema() : void
     {
         // isTypeOf used to resolve runtime type for Interface
         $petType = new InterfaceType([
@@ -141,7 +141,7 @@ class ExecutorLazySchemaTest extends TestCase
             $result->errors[0]->getMessage());
     }
 
-    public function testHintsOnConflictingTypeInstancesInDefinitions()
+    public function testHintsOnConflictingTypeInstancesInDefinitions() : void
     {
         $calls = [];
         $typeLoader = function($name) use (&$calls) {
@@ -197,7 +197,7 @@ class ExecutorLazySchemaTest extends TestCase
         );
     }
 
-    public function testSimpleQuery()
+    public function testSimpleQuery() : void
     {
         $schema = new Schema([
             'query' => $this->loadType('Query'),
@@ -225,7 +225,7 @@ class ExecutorLazySchemaTest extends TestCase
         $this->assertEquals($expectedExecutorCalls, $this->calls);
     }
 
-    public function testDeepQuery()
+    public function testDeepQuery() : void
     {
         $schema = new Schema([
             'query' => $this->loadType('Query'),
@@ -261,7 +261,7 @@ class ExecutorLazySchemaTest extends TestCase
         $this->assertEquals($expectedExecutorCalls, $this->calls);
     }
 
-    public function testResolveUnion()
+    public function testResolveUnion() : void
     {
         $schema = new Schema([
             'query' => $this->loadType('Query'),
diff --git a/tests/Executor/ExecutorSchemaTest.php b/tests/Executor/ExecutorSchemaTest.php
index 54c153b..5c62b09 100644
--- a/tests/Executor/ExecutorSchemaTest.php
+++ b/tests/Executor/ExecutorSchemaTest.php
@@ -15,7 +15,7 @@ class ExecutorSchemaTest extends TestCase
     /**
      * @see it('executes using a schema')
      */
-    public function testExecutesUsingASchema()
+    public function testExecutesUsingASchema() : void
     {
         $BlogArticle = null;
         $BlogImage = new ObjectType([
diff --git a/tests/Executor/ExecutorTest.php b/tests/Executor/ExecutorTest.php
index 4fa7efb..de63db2 100644
--- a/tests/Executor/ExecutorTest.php
+++ b/tests/Executor/ExecutorTest.php
@@ -28,7 +28,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('executes arbitrary code')
      */
-    public function testExecutesArbitraryCode()
+    public function testExecutesArbitraryCode() : void
     {
         $deepData = null;
         $data = null;
@@ -166,7 +166,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('merges parallel fragments')
      */
-    public function testMergesParallelFragments()
+    public function testMergesParallelFragments() : void
     {
         $ast = Parser::parse('
       { a, ...FragOne, ...FragTwo }
@@ -227,7 +227,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('provides info about current execution state')
      */
-    public function testProvidesInfoAboutCurrentExecutionState()
+    public function testProvidesInfoAboutCurrentExecutionState() : void
     {
         $ast = Parser::parse('query ($var: String) { result: test }');
 
@@ -279,7 +279,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('threads root value context correctly')
      */
-    public function testThreadsContextCorrectly()
+    public function testThreadsContextCorrectly() : void
     {
         // threads context correctly
         $doc = 'query Example { a }';
@@ -313,7 +313,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('correctly threads arguments')
      */
-    public function testCorrectlyThreadsArguments()
+    public function testCorrectlyThreadsArguments() : void
     {
         $doc = '
       query Example {
@@ -350,7 +350,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('nulls out error subtrees')
      */
-    public function testNullsOutErrorSubtrees()
+    public function testNullsOutErrorSubtrees() : void
     {
         $doc = '{
       sync
@@ -528,7 +528,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('uses the inline operation if no operation name is provided')
      */
-    public function testUsesTheInlineOperationIfNoOperationIsProvided()
+    public function testUsesTheInlineOperationIfNoOperationIsProvided() : void
     {
         $doc = '{ a }';
         $data = ['a' => 'b'];
@@ -550,7 +550,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('uses the only operation if no operation name is provided')
      */
-    public function testUsesTheOnlyOperationIfNoOperationIsProvided()
+    public function testUsesTheOnlyOperationIfNoOperationIsProvided() : void
     {
         $doc = 'query Example { a }';
         $data = [ 'a' => 'b' ];
@@ -571,7 +571,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('uses the named operation if operation name is provided')
      */
-    public function testUsesTheNamedOperationIfOperationNameIsProvided()
+    public function testUsesTheNamedOperationIfOperationNameIsProvided() : void
     {
         $doc = 'query Example { first: a } query OtherExample { second: a }';
         $data = [ 'a' => 'b' ];
@@ -592,7 +592,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('provides error if no operation is provided')
      */
-    public function testProvidesErrorIfNoOperationIsProvided()
+    public function testProvidesErrorIfNoOperationIsProvided() : void
     {
         $doc = 'fragment Example on Type { a }';
         $data = [ 'a' => 'b' ];
@@ -621,7 +621,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('errors if no op name is provided with multiple operations')
      */
-    public function testErrorsIfNoOperationIsProvidedWithMultipleOperations()
+    public function testErrorsIfNoOperationIsProvidedWithMultipleOperations() : void
     {
         $doc = 'query Example { a } query OtherExample { a }';
         $data = ['a' => 'b'];
@@ -651,7 +651,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('errors if unknown operation name is provided')
      */
-    public function testErrorsIfUnknownOperationNameIsProvided()
+    public function testErrorsIfUnknownOperationNameIsProvided() : void
     {
         $doc = 'query Example { a } query OtherExample { a }';
         $ast = Parser::parse($doc);
@@ -689,7 +689,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('uses the query schema for queries')
      */
-    public function testUsesTheQuerySchemaForQueries()
+    public function testUsesTheQuerySchemaForQueries() : void
     {
         $doc = 'query Q { a } mutation M { c }';
         $data = ['a' => 'b', 'c' => 'd'];
@@ -716,7 +716,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('uses the mutation schema for mutations')
      */
-    public function testUsesTheMutationSchemaForMutations()
+    public function testUsesTheMutationSchemaForMutations() : void
     {
         $doc = 'query Q { a } mutation M { c }';
         $data = [ 'a' => 'b', 'c' => 'd' ];
@@ -742,7 +742,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('uses the subscription schema for subscriptions')
      */
-    public function testUsesTheSubscriptionSchemaForSubscriptions()
+    public function testUsesTheSubscriptionSchemaForSubscriptions() : void
     {
         $doc = 'query Q { a } subscription S { a }';
         $data = [ 'a' => 'b', 'c' => 'd' ];
@@ -766,7 +766,7 @@ class ExecutorTest extends TestCase
         $this->assertEquals(['data' => ['a' => 'b']], $subscriptionResult->toArray());
     }
 
-    public function testCorrectFieldOrderingDespiteExecutionOrder()
+    public function testCorrectFieldOrderingDespiteExecutionOrder() : void
     {
         $doc = '{
       a,
@@ -823,7 +823,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('Avoids recursion')
      */
-    public function testAvoidsRecursion()
+    public function testAvoidsRecursion() : void
     {
         $doc = '
       query Q {
@@ -855,7 +855,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('does not include illegal fields in output')
      */
-    public function testDoesNotIncludeIllegalFieldsInOutput()
+    public function testDoesNotIncludeIllegalFieldsInOutput() : void
     {
         $doc = 'mutation M {
       thisIsIllegalDontIncludeMe
@@ -882,7 +882,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('does not include arguments that were not set')
      */
-    public function testDoesNotIncludeArgumentsThatWereNotSet()
+    public function testDoesNotIncludeArgumentsThatWereNotSet() : void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -917,7 +917,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('fails when an isTypeOf check is not met')
      */
-    public function testFailsWhenAnIsTypeOfCheckIsNotMet()
+    public function testFailsWhenAnIsTypeOfCheckIsNotMet() : void
     {
         $SpecialType = new ObjectType([
             'name' => 'SpecialType',
@@ -967,7 +967,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('executes ignoring invalid non-executable definitions')
      */
-    public function testExecutesIgnoringInvalidNonExecutableDefinitions()
+    public function testExecutesIgnoringInvalidNonExecutableDefinitions() : void
     {
         $query = Parser::parse('
       { foo }
@@ -999,7 +999,7 @@ class ExecutorTest extends TestCase
     /**
      * @see it('uses a custom field resolver')
      */
-    public function testUsesACustomFieldResolver()
+    public function testUsesACustomFieldResolver() : void
     {
         $query = Parser::parse('{ foo }');
 
@@ -1034,7 +1034,7 @@ class ExecutorTest extends TestCase
         $this->assertEquals($expected, $result->toArray());
     }
 
-    public function testSubstitutesArgumentWithDefaultValue()
+    public function testSubstitutesArgumentWithDefaultValue() : void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -1078,7 +1078,7 @@ class ExecutorTest extends TestCase
     /**
      * @see https://github.com/webonyx/graphql-php/issues/59
      */
-    public function testSerializesToEmptyObjectVsEmptyArray()
+    public function testSerializesToEmptyObjectVsEmptyArray() : void
     {
         $iface = null;
 
diff --git a/tests/Executor/LazyInterfaceTest.php b/tests/Executor/LazyInterfaceTest.php
index 73af88e..a099187 100644
--- a/tests/Executor/LazyInterfaceTest.php
+++ b/tests/Executor/LazyInterfaceTest.php
@@ -102,7 +102,7 @@ class LazyInterfaceTest extends TestCase
     /**
      * Handles execution of a lazily created interface
      */
-    public function testReturnsFragmentsWithLazyCreatedInterface()
+    public function testReturnsFragmentsWithLazyCreatedInterface() : void
     {
         $request = '
         {
diff --git a/tests/Executor/ListsTest.php b/tests/Executor/ListsTest.php
index f691a20..3ab1406 100644
--- a/tests/Executor/ListsTest.php
+++ b/tests/Executor/ListsTest.php
@@ -18,9 +18,9 @@ class ListsTest extends TestCase
     // Describe: Execute: Handles list nullability
 
     /**
-     * @describe [T]
+     * [T]
      */
-    public function testHandlesNullableListsWithArray()
+    public function testHandlesNullableListsWithArray() : void
     {
         // Contains values
         $this->checkHandlesNullableLists(
@@ -42,9 +42,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T]
+     * [T]
      */
-    public function testHandlesNullableListsWithPromiseArray()
+    public function testHandlesNullableListsWithPromiseArray() : void
     {
         // Contains values
         $this->checkHandlesNullableLists(
@@ -91,9 +91,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T]
+     * [T]
      */
-    public function testHandlesNullableListsWithArrayPromise()
+    public function testHandlesNullableListsWithArrayPromise() : void
     {
         // Contains values
         $this->checkHandlesNullableLists(
@@ -154,9 +154,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T]!
+     * [T]!
      */
-    public function testHandlesNonNullableListsWithArray()
+    public function testHandlesNonNullableListsWithArray() : void
     {
         // Contains values
         $this->checkHandlesNonNullableLists(
@@ -187,9 +187,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T]!
+     * [T]!
      */
-    public function testHandlesNonNullableListsWithPromiseArray()
+    public function testHandlesNonNullableListsWithPromiseArray() : void
     {
         // Contains values
         $this->checkHandlesNonNullableLists(
@@ -243,9 +243,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T]!
+     * [T]!
      */
-    public function testHandlesNonNullableListsWithArrayPromise()
+    public function testHandlesNonNullableListsWithArrayPromise() : void
     {
         // Contains values
         $this->checkHandlesNonNullableLists(
@@ -305,9 +305,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T!]
+     * [T!]
      */
-    public function testHandlesListOfNonNullsWithArray()
+    public function testHandlesListOfNonNullsWithArray() : void
     {
         // Contains values
         $this->checkHandlesListOfNonNulls(
@@ -338,9 +338,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T!]
+     * [T!]
      */
-    public function testHandlesListOfNonNullsWithPromiseArray()
+    public function testHandlesListOfNonNullsWithPromiseArray() : void
     {
         // Contains values
         $this->checkHandlesListOfNonNulls(
@@ -396,9 +396,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T]!
+     * [T]!
      */
-    public function testHandlesListOfNonNullsWithArrayPromise()
+    public function testHandlesListOfNonNullsWithArrayPromise() : void
     {
         // Contains values
         $this->checkHandlesListOfNonNulls(
@@ -452,9 +452,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T!]!
+     * [T!]!
      */
-    public function testHandlesNonNullListOfNonNullsWithArray()
+    public function testHandlesNonNullListOfNonNullsWithArray() : void
     {
         // Contains values
         $this->checkHandlesNonNullListOfNonNulls(
@@ -495,9 +495,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T!]!
+     * [T!]!
      */
-    public function testHandlesNonNullListOfNonNullsWithPromiseArray()
+    public function testHandlesNonNullListOfNonNullsWithPromiseArray() : void
     {
         // Contains values
         $this->checkHandlesNonNullListOfNonNulls(
@@ -562,9 +562,9 @@ class ListsTest extends TestCase
     }
 
     /**
-     * @describe [T!]!
+     * [T!]!
      */
-    public function testHandlesNonNullListOfNonNullsWithArrayPromise()
+    public function testHandlesNonNullListOfNonNullsWithArrayPromise() : void
     {
         // Contains values
         $this->checkHandlesNonNullListOfNonNulls(
diff --git a/tests/Executor/MutationsTest.php b/tests/Executor/MutationsTest.php
index 0abe2d6..bc83b5d 100644
--- a/tests/Executor/MutationsTest.php
+++ b/tests/Executor/MutationsTest.php
@@ -19,7 +19,7 @@ class MutationsTest extends TestCase
     /**
      * @see it('evaluates mutations serially')
      */
-    public function testEvaluatesMutationsSerially()
+    public function testEvaluatesMutationsSerially() : void
     {
         $doc = 'mutation M {
       first: immediatelyChangeTheNumber(newNumber: 1) {
@@ -65,7 +65,7 @@ class MutationsTest extends TestCase
     /**
      * @see it('evaluates mutations correctly in the presense of a failed mutation')
      */
-    public function testEvaluatesMutationsCorrectlyInThePresenseOfAFailedMutation()
+    public function testEvaluatesMutationsCorrectlyInThePresenseOfAFailedMutation() : void
     {
         $doc = 'mutation M {
       first: immediatelyChangeTheNumber(newNumber: 1) {
diff --git a/tests/Executor/NonNullTest.php b/tests/Executor/NonNullTest.php
index c93a041..2d2a528 100644
--- a/tests/Executor/NonNullTest.php
+++ b/tests/Executor/NonNullTest.php
@@ -132,7 +132,7 @@ class NonNullTest extends TestCase
     /**
      * @see it('nulls a nullable field that throws synchronously')
      */
-    public function testNullsANullableFieldThatThrowsSynchronously()
+    public function testNullsANullableFieldThatThrowsSynchronously() : void
     {
         $doc = '
       query Q {
@@ -156,7 +156,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->throwingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsANullableFieldThatThrowsInAPromise()
+    public function testNullsANullableFieldThatThrowsInAPromise() : void
     {
         $doc = '
       query Q {
@@ -181,7 +181,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->throwingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsASynchronouslyReturnedObjectThatContainsANonNullableFieldThatThrowsSynchronously()
+    public function testNullsASynchronouslyReturnedObjectThatContainsANonNullableFieldThatThrowsSynchronously() : void
     {
         // nulls a synchronously returned object that contains a non-nullable field that throws synchronously
         $doc = '
@@ -205,7 +205,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->throwingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsAsynchronouslyReturnedObjectThatContainsANonNullableFieldThatThrowsInAPromise()
+    public function testNullsAsynchronouslyReturnedObjectThatContainsANonNullableFieldThatThrowsInAPromise() : void
     {
         $doc = '
       query Q {
@@ -229,7 +229,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->throwingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsAnObjectReturnedInAPromiseThatContainsANonNullableFieldThatThrowsSynchronously()
+    public function testNullsAnObjectReturnedInAPromiseThatContainsANonNullableFieldThatThrowsSynchronously() : void
     {
         $doc = '
       query Q {
@@ -253,7 +253,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->throwingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsAnObjectReturnedInAPromiseThatContainsANonNullableFieldThatThrowsInAPromise()
+    public function testNullsAnObjectReturnedInAPromiseThatContainsANonNullableFieldThatThrowsInAPromise() : void
     {
         $doc = '
       query Q {
@@ -280,7 +280,7 @@ class NonNullTest extends TestCase
     /**
      * @see it('nulls a complex tree of nullable fields that throw')
      */
-    public function testNullsAComplexTreeOfNullableFieldsThatThrow()
+    public function testNullsAComplexTreeOfNullableFieldsThatThrow() : void
     {
         $doc = '
       query Q {
@@ -359,7 +359,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->throwingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsTheFirstNullableObjectAfterAFieldThrowsInALongChainOfFieldsThatAreNonNull()
+    public function testNullsTheFirstNullableObjectAfterAFieldThrowsInALongChainOfFieldsThatAreNonNull() : void
     {
         $doc = '
       query Q {
@@ -430,7 +430,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->throwingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsANullableFieldThatSynchronouslyReturnsNull()
+    public function testNullsANullableFieldThatSynchronouslyReturnsNull() : void
     {
         $doc = '
       query Q {
@@ -448,7 +448,7 @@ class NonNullTest extends TestCase
         $this->assertEquals($expected, Executor::execute($this->schema, $ast, $this->nullingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsANullableFieldThatReturnsNullInAPromise()
+    public function testNullsANullableFieldThatReturnsNullInAPromise() : void
     {
         $doc = '
       query Q {
@@ -467,7 +467,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->nullingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsASynchronouslyReturnedObjectThatContainsANonNullableFieldThatReturnsNullSynchronously()
+    public function testNullsASynchronouslyReturnedObjectThatContainsANonNullableFieldThatReturnsNullSynchronously() : void
     {
         $doc = '
       query Q {
@@ -493,7 +493,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->nullingData, null, [], 'Q')->toArray(true));
     }
 
-    public function testNullsASynchronouslyReturnedObjectThatContainsANonNullableFieldThatReturnsNullInAPromise()
+    public function testNullsASynchronouslyReturnedObjectThatContainsANonNullableFieldThatReturnsNullInAPromise() : void
     {
         $doc = '
       query Q {
@@ -523,7 +523,7 @@ class NonNullTest extends TestCase
         );
     }
 
-    public function testNullsAnObjectReturnedInAPromiseThatContainsANonNullableFieldThatReturnsNullSynchronously()
+    public function testNullsAnObjectReturnedInAPromiseThatContainsANonNullableFieldThatReturnsNullSynchronously() : void
     {
         $doc = '
       query Q {
@@ -553,7 +553,7 @@ class NonNullTest extends TestCase
         );
     }
 
-    public function testNullsAnObjectReturnedInAPromiseThatContainsANonNullableFieldThatReturnsNullInaAPromise()
+    public function testNullsAnObjectReturnedInAPromiseThatContainsANonNullableFieldThatReturnsNullInaAPromise() : void
     {
         $doc = '
       query Q {
@@ -583,7 +583,7 @@ class NonNullTest extends TestCase
         );
     }
 
-    public function testNullsAComplexTreeOfNullableFieldsThatReturnNull()
+    public function testNullsAComplexTreeOfNullableFieldsThatReturnNull() : void
     {
         $doc = '
       query Q {
@@ -649,7 +649,7 @@ class NonNullTest extends TestCase
         $this->assertEquals($expected, $actual);
     }
 
-    public function testNullsTheFirstNullableObjectAfterAFieldReturnsNullInALongChainOfFieldsThatAreNonNull()
+    public function testNullsTheFirstNullableObjectAfterAFieldReturnsNullInALongChainOfFieldsThatAreNonNull() : void
     {
         $doc = '
       query Q {
@@ -726,7 +726,7 @@ class NonNullTest extends TestCase
     /**
      * @see it('nulls the top level if sync non-nullable field throws')
      */
-    public function testNullsTheTopLevelIfSyncNonNullableFieldThrows()
+    public function testNullsTheTopLevelIfSyncNonNullableFieldThrows() : void
     {
         $doc = '
       query Q { syncNonNull }
@@ -741,7 +741,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, $actual);
     }
 
-    public function testNullsTheTopLevelIfAsyncNonNullableFieldErrors()
+    public function testNullsTheTopLevelIfAsyncNonNullableFieldErrors() : void
     {
         $doc = '
       query Q { promiseNonNull }
@@ -758,7 +758,7 @@ class NonNullTest extends TestCase
         $this->assertArraySubset($expected, Executor::execute($this->schema, $ast, $this->throwingData, null, [], 'Q')->toArray());
     }
 
-    public function testNullsTheTopLevelIfSyncNonNullableFieldReturnsNull()
+    public function testNullsTheTopLevelIfSyncNonNullableFieldReturnsNull() : void
     {
         // nulls the top level if sync non-nullable field returns null
         $doc = '
@@ -779,7 +779,7 @@ class NonNullTest extends TestCase
         );
     }
 
-    public function testNullsTheTopLevelIfAsyncNonNullableFieldResolvesNull()
+    public function testNullsTheTopLevelIfAsyncNonNullableFieldResolvesNull() : void
     {
         $doc = '
       query Q { promiseNonNull }
diff --git a/tests/Executor/Promise/ReactPromiseAdapterTest.php b/tests/Executor/Promise/ReactPromiseAdapterTest.php
index 294c11f..6859aeb 100644
--- a/tests/Executor/Promise/ReactPromiseAdapterTest.php
+++ b/tests/Executor/Promise/ReactPromiseAdapterTest.php
@@ -25,7 +25,7 @@ class ReactPromiseAdapterTest extends TestCase
         }
     }
 
-    public function testIsThenableReturnsTrueWhenAReactPromiseIsGiven()
+    public function testIsThenableReturnsTrueWhenAReactPromiseIsGiven() : void
     {
         $reactAdapter = new ReactPromiseAdapter();
 
@@ -43,7 +43,7 @@ class ReactPromiseAdapterTest extends TestCase
         $this->assertSame(false, $reactAdapter->isThenable(new \stdClass()));
     }
 
-    public function testConvertsReactPromisesToGraphQlOnes()
+    public function testConvertsReactPromisesToGraphQlOnes() : void
     {
         $reactAdapter = new ReactPromiseAdapter();
         $reactPromise = new FulfilledPromise(1);
@@ -54,7 +54,7 @@ class ReactPromiseAdapterTest extends TestCase
         $this->assertInstanceOf('React\Promise\FulfilledPromise', $promise->adoptedPromise);
     }
 
-    public function testThen()
+    public function testThen() : void
     {
         $reactAdapter = new ReactPromiseAdapter();
         $reactPromise = new FulfilledPromise(1);
@@ -71,7 +71,7 @@ class ReactPromiseAdapterTest extends TestCase
         $this->assertInstanceOf('React\Promise\FulfilledPromise', $resultPromise->adoptedPromise);
     }
 
-    public function testCreate()
+    public function testCreate() : void
     {
         $reactAdapter = new ReactPromiseAdapter();
         $resolvedPromise = $reactAdapter->create(function ($resolve) {
@@ -90,7 +90,7 @@ class ReactPromiseAdapterTest extends TestCase
         $this->assertSame(1, $result);
     }
 
-    public function testCreateFulfilled()
+    public function testCreateFulfilled() : void
     {
         $reactAdapter = new ReactPromiseAdapter();
         $fulfilledPromise = $reactAdapter->createFulfilled(1);
@@ -107,7 +107,7 @@ class ReactPromiseAdapterTest extends TestCase
         $this->assertSame(1, $result);
     }
 
-    public function testCreateRejected()
+    public function testCreateRejected() : void
     {
         $reactAdapter = new ReactPromiseAdapter();
         $rejectedPromise = $reactAdapter->createRejected(new \Exception('I am a bad promise'));
@@ -125,7 +125,7 @@ class ReactPromiseAdapterTest extends TestCase
         $this->assertEquals('I am a bad promise', $exception->getMessage());
     }
 
-    public function testAll()
+    public function testAll() : void
     {
         $reactAdapter = new ReactPromiseAdapter();
         $promises = [new FulfilledPromise(1), new FulfilledPromise(2), new FulfilledPromise(3)];
@@ -144,7 +144,7 @@ class ReactPromiseAdapterTest extends TestCase
         $this->assertSame([1, 2, 3], $result);
     }
 
-    public function testAllShouldPreserveTheOrderOfTheArrayWhenResolvingAsyncPromises()
+    public function testAllShouldPreserveTheOrderOfTheArrayWhenResolvingAsyncPromises() : void
     {
         $reactAdapter = new ReactPromiseAdapter();
         $deferred = new Deferred();
diff --git a/tests/Executor/Promise/SyncPromiseAdapterTest.php b/tests/Executor/Promise/SyncPromiseAdapterTest.php
index 5aabf9d..bbe838b 100644
--- a/tests/Executor/Promise/SyncPromiseAdapterTest.php
+++ b/tests/Executor/Promise/SyncPromiseAdapterTest.php
@@ -20,7 +20,7 @@ class SyncPromiseAdapterTest extends TestCase
         $this->promises = new SyncPromiseAdapter();
     }
 
-    public function testIsThenable()
+    public function testIsThenable() : void
     {
         $this->assertEquals(true, $this->promises->isThenable(new Deferred(function() {})));
         $this->assertEquals(false, $this->promises->isThenable(false));
@@ -33,7 +33,7 @@ class SyncPromiseAdapterTest extends TestCase
         $this->assertEquals(false, $this->promises->isThenable(new \stdClass()));
     }
 
-    public function testConvert()
+    public function testConvert() : void
     {
         $dfd = new Deferred(function() {});
         $result = $this->promises->convertThenable($dfd);
@@ -46,7 +46,7 @@ class SyncPromiseAdapterTest extends TestCase
         $this->promises->convertThenable('');
     }
 
-    public function testThen()
+    public function testThen() : void
     {
         $dfd = new Deferred(function() {});
         $promise = $this->promises->convertThenable($dfd);
@@ -57,7 +57,7 @@ class SyncPromiseAdapterTest extends TestCase
         $this->assertInstanceOf('GraphQL\Executor\Promise\Adapter\SyncPromise', $result->adoptedPromise);
     }
 
-    public function testCreatePromise()
+    public function testCreatePromise() : void
     {
         $promise = $this->promises->create(function($resolve, $reject) {});
 
@@ -71,19 +71,19 @@ class SyncPromiseAdapterTest extends TestCase
         $this->assertValidPromise($promise, null, 'A', SyncPromise::FULFILLED);
     }
 
-    public function testCreateFulfilledPromise()
+    public function testCreateFulfilledPromise() : void
     {
         $promise = $this->promises->createFulfilled('test');
         $this->assertValidPromise($promise, null, 'test', SyncPromise::FULFILLED);
     }
 
-    public function testCreateRejectedPromise()
+    public function testCreateRejectedPromise() : void
     {
         $promise = $this->promises->createRejected(new \Exception('test reason'));
         $this->assertValidPromise($promise, 'test reason', null, SyncPromise::REJECTED);
     }
 
-    public function testCreatePromiseAll()
+    public function testCreatePromiseAll() : void
     {
         $promise = $this->promises->all([]);
         $this->assertValidPromise($promise, null, [], SyncPromise::FULFILLED);
@@ -117,7 +117,7 @@ class SyncPromiseAdapterTest extends TestCase
         $this->assertValidPromise($promise, null, ['1', 'value1', 'value2', 3, 'value2-value3', []], SyncPromise::FULFILLED);
     }
 
-    public function testWait()
+    public function testWait() : void
     {
         $called = [];
 
diff --git a/tests/Executor/Promise/SyncPromiseTest.php b/tests/Executor/Promise/SyncPromiseTest.php
index d8f0840..6c878aa 100644
--- a/tests/Executor/Promise/SyncPromiseTest.php
+++ b/tests/Executor/Promise/SyncPromiseTest.php
@@ -258,7 +258,7 @@ class SyncPromiseTest extends TestCase
         $this->assertValidPromise($nextPromise3, $expectedNextReason, $expectedNextValue, $expectedNextState);
     }
 
-    public function testPendingPromise()
+    public function testPendingPromise() : void
     {
         $promise = new SyncPromise();
         $this->assertEquals(SyncPromise::PENDING, $promise->state);
@@ -319,7 +319,7 @@ class SyncPromiseTest extends TestCase
         $this->assertValidPromise($promise2, "Rejected Once Again", null, SyncPromise::REJECTED);
     }
 
-    public function testPendingPromiseThen()
+    public function testPendingPromiseThen() : void
     {
         $promise = new SyncPromise();
         $this->assertEquals(SyncPromise::PENDING, $promise->state);
diff --git a/tests/Executor/ResolveTest.php b/tests/Executor/ResolveTest.php
index b5f6288..0d05e53 100644
--- a/tests/Executor/ResolveTest.php
+++ b/tests/Executor/ResolveTest.php
@@ -28,7 +28,7 @@ class ResolveTest extends TestCase
     /**
      * @see it('default function accesses properties')
      */
-    public function testDefaultFunctionAccessesProperties()
+    public function testDefaultFunctionAccessesProperties() : void
     {
         $schema = $this->buildSchema(['type' => Type::string()]);
 
@@ -45,7 +45,7 @@ class ResolveTest extends TestCase
     /**
      * @see it('default function calls methods')
      */
-    public function testDefaultFunctionCallsClosures()
+    public function testDefaultFunctionCallsClosures() : void
     {
         $schema = $this->buildSchema(['type' => Type::string()]);
         $_secret = 'secretValue' . uniqid();
@@ -64,7 +64,7 @@ class ResolveTest extends TestCase
     /**
      * @see it('default function passes args and context')
      */
-    public function testDefaultFunctionPassesArgsAndContext()
+    public function testDefaultFunctionPassesArgsAndContext() : void
     {
         $schema = $this->buildSchema([
             'type' => Type::int(),
@@ -82,7 +82,7 @@ class ResolveTest extends TestCase
     /**
      * @see it('uses provided resolve function')
      */
-    public function testUsesProvidedResolveFunction()
+    public function testUsesProvidedResolveFunction() : void
     {
         $schema = $this->buildSchema([
             'type' => Type::string(),
diff --git a/tests/Executor/SyncTest.php b/tests/Executor/SyncTest.php
index 988c8a6..3c1c989 100644
--- a/tests/Executor/SyncTest.php
+++ b/tests/Executor/SyncTest.php
@@ -68,7 +68,7 @@ class SyncTest extends TestCase
     /**
      * @see it('does not return a Promise for initial errors')
      */
-    public function testDoesNotReturnAPromiseForInitialErrors()
+    public function testDoesNotReturnAPromiseForInitialErrors() : void
     {
         $doc = 'fragment Example on Query { syncField }';
         $result = $this->execute(
@@ -82,7 +82,7 @@ class SyncTest extends TestCase
     /**
      * @see it('does not return a Promise if fields are all synchronous')
      */
-    public function testDoesNotReturnAPromiseIfFieldsAreAllSynchronous()
+    public function testDoesNotReturnAPromiseIfFieldsAreAllSynchronous() : void
     {
         $doc = 'query Example { syncField }';
         $result = $this->execute(
@@ -96,7 +96,7 @@ class SyncTest extends TestCase
     /**
      * @see it('does not return a Promise if mutation fields are all synchronous')
      */
-    public function testDoesNotReturnAPromiseIfMutationFieldsAreAllSynchronous()
+    public function testDoesNotReturnAPromiseIfMutationFieldsAreAllSynchronous() : void
     {
         $doc = 'mutation Example { syncMutationField }';
         $result = $this->execute(
@@ -110,7 +110,7 @@ class SyncTest extends TestCase
     /**
      * @see it('returns a Promise if any field is asynchronous')
      */
-    public function testReturnsAPromiseIfAnyFieldIsAsynchronous()
+    public function testReturnsAPromiseIfAnyFieldIsAsynchronous() : void
     {
         $doc = 'query Example { syncField, asyncField }';
         $result = $this->execute(
@@ -126,7 +126,7 @@ class SyncTest extends TestCase
     /**
      * @see it('does not return a Promise for syntax errors')
      */
-    public function testDoesNotReturnAPromiseForSyntaxErrors()
+    public function testDoesNotReturnAPromiseForSyntaxErrors() : void
     {
         $doc = 'fragment Example on Query { { { syncField }';
         $result = $this->graphqlSync(
@@ -144,7 +144,7 @@ class SyncTest extends TestCase
     /**
      * @see it('does not return a Promise for validation errors')
      */
-    public function testDoesNotReturnAPromiseForValidationErrors()
+    public function testDoesNotReturnAPromiseForValidationErrors() : void
     {
         $doc = 'fragment Example on Query { unknownField }';
         $validationErrors = DocumentValidator::validate($this->schema, Parser::parse($doc));
@@ -163,7 +163,7 @@ class SyncTest extends TestCase
     /**
      * @see it('does not return a Promise for sync execution')
      */
-    public function testDoesNotReturnAPromiseForSyncExecution()
+    public function testDoesNotReturnAPromiseForSyncExecution() : void
     {
         $doc = 'query Example { syncField }';
         $result = $this->graphqlSync(
diff --git a/tests/Executor/UnionInterfaceTest.php b/tests/Executor/UnionInterfaceTest.php
index 59919a6..4d1d934 100644
--- a/tests/Executor/UnionInterfaceTest.php
+++ b/tests/Executor/UnionInterfaceTest.php
@@ -99,7 +99,7 @@ class UnionInterfaceTest extends TestCase
     /**
      * @see it('can introspect on union and intersection types')
      */
-    public function testCanIntrospectOnUnionAndIntersectionTypes()
+    public function testCanIntrospectOnUnionAndIntersectionTypes() : void
     {
 
         $ast = Parser::parse('
@@ -162,7 +162,7 @@ class UnionInterfaceTest extends TestCase
     /**
      * @see it('executes using union types')
      */
-    public function testExecutesUsingUnionTypes()
+    public function testExecutesUsingUnionTypes() : void
     {
         // NOTE: This is an *invalid* query, but it should be an *executable* query.
         $ast = Parser::parse('
@@ -194,7 +194,7 @@ class UnionInterfaceTest extends TestCase
     /**
      * @see it('executes union types with inline fragments')
      */
-    public function testExecutesUnionTypesWithInlineFragments()
+    public function testExecutesUnionTypesWithInlineFragments() : void
     {
         // This is the valid version of the query in the above test.
         $ast = Parser::parse('
@@ -231,7 +231,7 @@ class UnionInterfaceTest extends TestCase
     /**
      * @see it('executes using interface types')
      */
-    public function testExecutesUsingInterfaceTypes()
+    public function testExecutesUsingInterfaceTypes() : void
     {
         // NOTE: This is an *invalid* query, but it should be an *executable* query.
         $ast = Parser::parse('
@@ -263,7 +263,7 @@ class UnionInterfaceTest extends TestCase
     /**
      * @see it('executes interface types with inline fragments')
      */
-    public function testExecutesInterfaceTypesWithInlineFragments()
+    public function testExecutesInterfaceTypesWithInlineFragments() : void
     {
         // This is the valid version of the query in the above test.
         $ast = Parser::parse('
@@ -299,7 +299,7 @@ class UnionInterfaceTest extends TestCase
     /**
      * @see it('allows fragment conditions to be abstract types')
      */
-    public function testAllowsFragmentConditionsToBeAbstractTypes()
+    public function testAllowsFragmentConditionsToBeAbstractTypes() : void
     {
         $ast = Parser::parse('
       {
@@ -354,7 +354,7 @@ class UnionInterfaceTest extends TestCase
     /**
      * @see it('gets execution info in resolver')
      */
-    public function testGetsExecutionInfoInResolver()
+    public function testGetsExecutionInfoInResolver() : void
     {
         $encounteredContext = null;
         $encounteredSchema = null;
diff --git a/tests/Executor/ValuesTest.php b/tests/Executor/ValuesTest.php
index 4f8f8fa..4d7bf2d 100644
--- a/tests/Executor/ValuesTest.php
+++ b/tests/Executor/ValuesTest.php
@@ -13,7 +13,7 @@ use PHPUnit\Framework\TestCase;
 
 class ValuesTest extends TestCase
 {
-    public function testGetIDVariableValues()
+    public function testGetIDVariableValues() : void
     {
         $this->expectInputVariablesMatchOutputVariables(['idInput' => '123456789']);
         $this->assertEquals(
@@ -23,13 +23,13 @@ class ValuesTest extends TestCase
         );
     }
 
-    public function testGetBooleanVariableValues()
+    public function testGetBooleanVariableValues() : void
     {
         $this->expectInputVariablesMatchOutputVariables(['boolInput' => true]);
         $this->expectInputVariablesMatchOutputVariables(['boolInput' => false]);
     }
 
-    public function testGetIntVariableValues()
+    public function testGetIntVariableValues() : void
     {
         $this->expectInputVariablesMatchOutputVariables(['intInput' => -1]);
         $this->expectInputVariablesMatchOutputVariables(['intInput' => 0]);
@@ -40,7 +40,7 @@ class ValuesTest extends TestCase
         $this->expectInputVariablesMatchOutputVariables(['intInput' => -2147483648]);
     }
 
-    public function testGetStringVariableValues()
+    public function testGetStringVariableValues() : void
     {
         $this->expectInputVariablesMatchOutputVariables(['stringInput' => 'meow']);
         $this->expectInputVariablesMatchOutputVariables(['stringInput' => '']);
@@ -50,7 +50,7 @@ class ValuesTest extends TestCase
         $this->expectInputVariablesMatchOutputVariables(['stringInput' => '1.2']);
     }
 
-    public function testGetFloatVariableValues()
+    public function testGetFloatVariableValues() : void
     {
         $this->expectInputVariablesMatchOutputVariables(['floatInput' => 1.2]);
         $this->expectInputVariablesMatchOutputVariables(['floatInput' => 1.0]);
@@ -59,42 +59,42 @@ class ValuesTest extends TestCase
         $this->expectInputVariablesMatchOutputVariables(['floatInput' => 1e3]);
     }
 
-    public function testBooleanForIDVariableThrowsError()
+    public function testBooleanForIDVariableThrowsError() : void
     {
         $this->expectGraphQLError(['idInput' => true]);
     }
 
-    public function testFloatForIDVariableThrowsError()
+    public function testFloatForIDVariableThrowsError() : void
     {
         $this->expectGraphQLError(['idInput' => 1.0]);
     }
 
-    public function testStringForBooleanVariableThrowsError()
+    public function testStringForBooleanVariableThrowsError() : void
     {
         $this->expectGraphQLError(['boolInput' => 'true']);
     }
 
-    public function testIntForBooleanVariableThrowsError()
+    public function testIntForBooleanVariableThrowsError() : void
     {
         $this->expectGraphQLError(['boolInput' => 1]);
     }
 
-    public function testFloatForBooleanVariableThrowsError()
+    public function testFloatForBooleanVariableThrowsError() : void
     {
         $this->expectGraphQLError(['boolInput' => 1.0]);
     }
 
-    public function testStringForIntVariableThrowsError()
+    public function testStringForIntVariableThrowsError() : void
     {
         $this->expectGraphQLError(['intInput' => 'true']);
     }
 
-    public function testPositiveBigIntForIntVariableThrowsError()
+    public function testPositiveBigIntForIntVariableThrowsError() : void
     {
         $this->expectGraphQLError(['intInput' => 2147483648]);
     }
 
-    public function testNegativeBigIntForIntVariableThrowsError()
+    public function testNegativeBigIntForIntVariableThrowsError() : void
     {
         $this->expectGraphQLError(['intInput' => -2147483649]);
     }
diff --git a/tests/Executor/VariablesTest.php b/tests/Executor/VariablesTest.php
index abf57aa..89392d2 100644
--- a/tests/Executor/VariablesTest.php
+++ b/tests/Executor/VariablesTest.php
@@ -12,15 +12,14 @@ use GraphQL\Type\Definition\ObjectType;
 use GraphQL\Type\Definition\Type;
 use PHPUnit\Framework\TestCase;
 
+/**
+ * Execute: Handles inputs
+ * Handles objects and nullability
+ */
 class VariablesTest extends TestCase
 {
-    // Execute: Handles inputs
-    // Handles objects and nullability
 
-    /**
-     * @describe using inline structs
-     */
-    public function testUsingInlineStructs()
+    public function testUsingInlineStructs() : void
     {
         // executes with complex input:
         $result = $this->executeQuery('
@@ -95,10 +94,7 @@ class VariablesTest extends TestCase
         );
     }
 
-    /**
-     * @describe using variables
-     */
-    public function testUsingVariables()
+    public function testUsingVariables() : void
     {
         $doc = '
             query q($input:TestInputObject) {
@@ -249,7 +245,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows nullable inputs to be omitted')
      */
-    public function testAllowsNullableInputsToBeOmitted()
+    public function testAllowsNullableInputsToBeOmitted() : void
     {
         $result = $this->executeQuery('
       {
@@ -266,7 +262,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows nullable inputs to be omitted in a variable')
      */
-    public function testAllowsNullableInputsToBeOmittedInAVariable()
+    public function testAllowsNullableInputsToBeOmittedInAVariable() : void
     {
         $result = $this->executeQuery('
       query SetsNullable($value: String) {
@@ -281,7 +277,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows nullable inputs to be omitted in an unlisted variable')
      */
-    public function testAllowsNullableInputsToBeOmittedInAnUnlistedVariable()
+    public function testAllowsNullableInputsToBeOmittedInAnUnlistedVariable() : void
     {
         $result = $this->executeQuery('
       query SetsNullable {
@@ -295,7 +291,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows nullable inputs to be set to null in a variable')
      */
-    public function testAllowsNullableInputsToBeSetToNullInAVariable()
+    public function testAllowsNullableInputsToBeSetToNullInAVariable() : void
     {
         $result = $this->executeQuery('
       query SetsNullable($value: String) {
@@ -310,7 +306,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows nullable inputs to be set to a value in a variable')
      */
-    public function testAllowsNullableInputsToBeSetToAValueInAVariable()
+    public function testAllowsNullableInputsToBeSetToAValueInAVariable() : void
     {
         $doc = '
       query SetsNullable($value: String) {
@@ -325,7 +321,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows nullable inputs to be set to a value directly')
      */
-    public function testAllowsNullableInputsToBeSetToAValueDirectly()
+    public function testAllowsNullableInputsToBeSetToAValueDirectly() : void
     {
         $result = $this->executeQuery('
       {
@@ -342,7 +338,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows non-nullable inputs to be omitted given a default')
      */
-    public function testAllowsNonNullableInputsToBeOmittedGivenADefault()
+    public function testAllowsNonNullableInputsToBeOmittedGivenADefault() : void
     {
         $result = $this->executeQuery('
         query SetsNonNullable($value: String = "default") {
@@ -358,7 +354,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('does not allow non-nullable inputs to be omitted in a variable')
      */
-    public function testDoesntAllowNonNullableInputsToBeOmittedInAVariable()
+    public function testDoesntAllowNonNullableInputsToBeOmittedInAVariable() : void
     {
         $result = $this->executeQuery('
         query SetsNonNullable($value: String!) {
@@ -381,7 +377,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('does not allow non-nullable inputs to be set to null in a variable')
      */
-    public function testDoesNotAllowNonNullableInputsToBeSetToNullInAVariable()
+    public function testDoesNotAllowNonNullableInputsToBeSetToNullInAVariable() : void
     {
         $doc = '
         query SetsNonNullable($value: String!) {
@@ -406,7 +402,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows non-nullable inputs to be set to a value in a variable')
      */
-    public function testAllowsNonNullableInputsToBeSetToAValueInAVariable()
+    public function testAllowsNonNullableInputsToBeSetToAValueInAVariable() : void
     {
         $doc = '
         query SetsNonNullable($value: String!) {
@@ -421,7 +417,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows non-nullable inputs to be set to a value directly')
      */
-    public function testAllowsNonNullableInputsToBeSetToAValueDirectly()
+    public function testAllowsNonNullableInputsToBeSetToAValueDirectly() : void
     {
         $result = $this->executeQuery('
       {
@@ -435,7 +431,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('reports error for missing non-nullable inputs')
      */
-    public function testReportsErrorForMissingNonNullableInputs()
+    public function testReportsErrorForMissingNonNullableInputs() : void
     {
         $result = $this->executeQuery('
       {
@@ -457,7 +453,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('reports error for array passed into string input')
      */
-    public function testReportsErrorForArrayPassedIntoStringInput()
+    public function testReportsErrorForArrayPassedIntoStringInput() : void
     {
 
         $doc = '
@@ -485,7 +481,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('serializing an array via GraphQLString throws TypeError')
      */
-    public function testSerializingAnArrayViaGraphQLStringThrowsTypeError()
+    public function testSerializingAnArrayViaGraphQLStringThrowsTypeError() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('String cannot represent non scalar value: [1,2,3]');
@@ -495,7 +491,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('reports error for non-provided variables for non-nullable inputs')
      */
-    public function testReportsErrorForNonProvidedVariablesForNonNullableInputs()
+    public function testReportsErrorForNonProvidedVariablesForNonNullableInputs() : void
     {
         // Note: this test would typically fail validation before encountering
         // this execution error, however for queries which previously validated
@@ -526,7 +522,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows lists to be null')
      */
-    public function testAllowsListsToBeNull()
+    public function testAllowsListsToBeNull() : void
     {
         $doc = '
         query q($input:[String]) {
@@ -542,7 +538,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows lists to contain values')
      */
-    public function testAllowsListsToContainValues()
+    public function testAllowsListsToContainValues() : void
     {
         $doc = '
         query q($input:[String]) {
@@ -557,7 +553,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows lists to contain null')
      */
-    public function testAllowsListsToContainNull()
+    public function testAllowsListsToContainNull() : void
     {
         $doc = '
         query q($input:[String]) {
@@ -572,7 +568,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('does not allow non-null lists to be null')
      */
-    public function testDoesNotAllowNonNullListsToBeNull()
+    public function testDoesNotAllowNonNullListsToBeNull() : void
     {
         $doc = '
         query q($input:[String]!) {
@@ -597,7 +593,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows non-null lists to contain values')
      */
-    public function testAllowsNonNullListsToContainValues()
+    public function testAllowsNonNullListsToContainValues() : void
     {
         $doc = '
         query q($input:[String]!) {
@@ -612,7 +608,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows non-null lists to contain null')
      */
-    public function testAllowsNonNullListsToContainNull()
+    public function testAllowsNonNullListsToContainNull() : void
     {
         $doc = '
         query q($input:[String]!) {
@@ -627,7 +623,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows lists of non-nulls to be null')
      */
-    public function testAllowsListsOfNonNullsToBeNull()
+    public function testAllowsListsOfNonNullsToBeNull() : void
     {
         $doc = '
         query q($input:[String!]) {
@@ -642,7 +638,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows lists of non-nulls to contain values')
      */
-    public function testAllowsListsOfNonNullsToContainValues()
+    public function testAllowsListsOfNonNullsToContainValues() : void
     {
         $doc = '
         query q($input:[String!]) {
@@ -657,7 +653,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('does not allow lists of non-nulls to contain null')
      */
-    public function testDoesNotAllowListsOfNonNullsToContainNull()
+    public function testDoesNotAllowListsOfNonNullsToContainNull() : void
     {
         $doc = '
         query q($input:[String!]) {
@@ -682,7 +678,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('does not allow non-null lists of non-nulls to be null')
      */
-    public function testDoesNotAllowNonNullListsOfNonNullsToBeNull()
+    public function testDoesNotAllowNonNullListsOfNonNullsToBeNull() : void
     {
         $doc = '
         query q($input:[String!]!) {
@@ -707,7 +703,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('allows non-null lists of non-nulls to contain values')
      */
-    public function testAllowsNonNullListsOfNonNullsToContainValues()
+    public function testAllowsNonNullListsOfNonNullsToContainValues() : void
     {
         $doc = '
         query q($input:[String!]!) {
@@ -722,7 +718,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('does not allow non-null lists of non-nulls to contain null')
      */
-    public function testDoesNotAllowNonNullListsOfNonNullsToContainNull()
+    public function testDoesNotAllowNonNullListsOfNonNullsToContainNull() : void
     {
         $doc = '
         query q($input:[String!]!) {
@@ -747,7 +743,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('does not allow invalid types to be used as values')
      */
-    public function testDoesNotAllowInvalidTypesToBeUsedAsValues()
+    public function testDoesNotAllowInvalidTypesToBeUsedAsValues() : void
     {
         $doc = '
         query q($input: TestType!) {
@@ -773,7 +769,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('does not allow unknown types to be used as values')
      */
-    public function testDoesNotAllowUnknownTypesToBeUsedAsValues()
+    public function testDoesNotAllowUnknownTypesToBeUsedAsValues() : void
     {
         $doc = '
         query q($input: UnknownType!) {
@@ -801,7 +797,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('when no argument provided')
      */
-    public function testWhenNoArgumentProvided()
+    public function testWhenNoArgumentProvided() : void
     {
         $result = $this->executeQuery('{
         fieldWithDefaultArgumentValue
@@ -816,7 +812,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('when omitted variable provided')
      */
-    public function testWhenOmittedVariableProvided()
+    public function testWhenOmittedVariableProvided() : void
     {
         $result = $this->executeQuery('query optionalVariable($optional: String) {
             fieldWithDefaultArgumentValue(input: $optional)
@@ -831,7 +827,7 @@ class VariablesTest extends TestCase
     /**
      * @see it('not when argument cannot be coerced')
      */
-    public function testNotWhenArgumentCannotBeCoerced()
+    public function testNotWhenArgumentCannotBeCoerced() : void
     {
         $result = $this->executeQuery('{
             fieldWithDefaultArgumentValue(input: WRONG_TYPE)
diff --git a/tests/Language/LexerTest.php b/tests/Language/LexerTest.php
index 898f1c6..a109232 100644
--- a/tests/Language/LexerTest.php
+++ b/tests/Language/LexerTest.php
@@ -14,7 +14,7 @@ class LexerTest extends TestCase
     /**
      * @see it('disallows uncommon control characters')
      */
-    public function testDissallowsUncommonControlCharacters()
+    public function testDissallowsUncommonControlCharacters() : void
     {
         $this->expectSyntaxError(
             Utils::chr(0x0007),
@@ -26,7 +26,7 @@ class LexerTest extends TestCase
     /**
      * @see it('accepts BOM header')
      */
-    public function testAcceptsBomHeader()
+    public function testAcceptsBomHeader() : void
     {
         $bom = Utils::chr(0xFEFF);
         $expected = [
@@ -42,7 +42,7 @@ class LexerTest extends TestCase
     /**
      * @see it('records line and column')
      */
-    public function testRecordsLineAndColumn()
+    public function testRecordsLineAndColumn() : void
     {
         $expected = [
             'kind' => Token::NAME,
@@ -58,7 +58,7 @@ class LexerTest extends TestCase
     /**
      * @see it('skips whitespace and comments')
      */
-    public function testSkipsWhitespacesAndComments()
+    public function testSkipsWhitespacesAndComments() : void
     {
         $example1 = '
 
@@ -101,7 +101,7 @@ class LexerTest extends TestCase
     /**
      * @see it('errors respect whitespace')
      */
-    public function testErrorsRespectWhitespace()
+    public function testErrorsRespectWhitespace() : void
     {
         $str = '' .
             "\n" .
@@ -129,7 +129,7 @@ class LexerTest extends TestCase
     /**
      * @see it('updates line numbers in error for file context')
      */
-    public function testUpdatesLineNumbersInErrorForFileContext()
+    public function testUpdatesLineNumbersInErrorForFileContext() : void
     {
         $str = '' .
             "\n" .
@@ -156,7 +156,7 @@ class LexerTest extends TestCase
         }
     }
 
-    public function testUpdatesColumnNumbersInErrorForFileContext()
+    public function testUpdatesColumnNumbersInErrorForFileContext() : void
     {
         $source = new Source('?', 'foo.js', new SourceLocation(1, 5));
 
@@ -179,7 +179,7 @@ class LexerTest extends TestCase
     /**
      * @see it('lexes strings')
      */
-    public function testLexesStrings()
+    public function testLexesStrings() : void
     {
         $this->assertArraySubset([
             'kind' => Token::STRING,
@@ -243,7 +243,7 @@ class LexerTest extends TestCase
     /**
      * @see it('lexes block strings')
      */
-    public function testLexesBlockString()
+    public function testLexesBlockString() : void
     {
         $this->assertArraySubset([
             'kind' => Token::BLOCK_STRING,
@@ -338,7 +338,7 @@ class LexerTest extends TestCase
      * @dataProvider reportsUsefulStringErrors
      * @see it('lex reports useful string errors')
      */
-    public function testLexReportsUsefulStringErrors($str, $expectedMessage, $location)
+    public function testLexReportsUsefulStringErrors($str, $expectedMessage, $location) : void
     {
         $this->expectSyntaxError($str, $expectedMessage, $location);
     }
@@ -356,7 +356,7 @@ class LexerTest extends TestCase
      * @dataProvider reportsUsefulBlockStringErrors
      * @see it('lex reports useful block string errors')
      */
-    public function testReportsUsefulBlockStringErrors($str, $expectedMessage, $location)
+    public function testReportsUsefulBlockStringErrors($str, $expectedMessage, $location) : void
     {
         $this->expectSyntaxError($str, $expectedMessage, $location);
     }
@@ -364,7 +364,7 @@ class LexerTest extends TestCase
     /**
      * @see it('lexes numbers')
      */
-    public function testLexesNumbers()
+    public function testLexesNumbers() : void
     {
         $this->assertArraySubset(
             ['kind' => Token::INT, 'start' => 0, 'end' => 1, 'value' => '4'],
@@ -451,7 +451,7 @@ class LexerTest extends TestCase
      * @dataProvider reportsUsefulNumberErrors
      * @see it('lex reports useful number errors')
      */
-    public function testReportsUsefulNumberErrors($str, $expectedMessage, $location)
+    public function testReportsUsefulNumberErrors($str, $expectedMessage, $location) : void
     {
         $this->expectSyntaxError($str, $expectedMessage, $location);
     }
@@ -459,7 +459,7 @@ class LexerTest extends TestCase
     /**
      * @see it('lexes punctuation')
      */
-    public function testLexesPunctuation()
+    public function testLexesPunctuation() : void
     {
         $this->assertArraySubset(
             ['kind' => Token::BANG, 'start' => 0, 'end' => 1, 'value' => null],
@@ -532,7 +532,7 @@ class LexerTest extends TestCase
      * @dataProvider reportsUsefulUnknownCharErrors
      * @see it('lex reports useful unknown character error')
      */
-    public function testReportsUsefulUnknownCharErrors($str, $expectedMessage, $location)
+    public function testReportsUsefulUnknownCharErrors($str, $expectedMessage, $location) : void
     {
         $this->expectSyntaxError($str, $expectedMessage, $location);
     }
@@ -540,7 +540,7 @@ class LexerTest extends TestCase
     /**
      * @see it('lex reports useful information for dashes in names')
      */
-    public function testReportsUsefulDashesInfo()
+    public function testReportsUsefulDashesInfo() : void
     {
         $q = 'a-b';
         $lexer = new Lexer(new Source($q));
@@ -560,7 +560,7 @@ class LexerTest extends TestCase
     /**
      * @see it('produces double linked list of tokens, including comments')
      */
-    public function testDoubleLinkedList()
+    public function testDoubleLinkedList() : void
     {
         $lexer = new Lexer(new Source('{
       #comment
diff --git a/tests/Language/ParserTest.php b/tests/Language/ParserTest.php
index b62a7eb..c50ecfb 100644
--- a/tests/Language/ParserTest.php
+++ b/tests/Language/ParserTest.php
@@ -19,21 +19,21 @@ use PHPUnit\Framework\TestCase;
 
 class ParserTest extends TestCase
 {
-    public function testAssertsThatASourceToParseIsNotNull()
+    public function testAssertsThatASourceToParseIsNotNull() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage('GraphQL query body is expected to be string, but got NULL');
         Parser::parse(null);
     }
 
-    public function testAssertsThatASourceToParseIsNotArray()
+    public function testAssertsThatASourceToParseIsNotArray() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage('GraphQL query body is expected to be string, but got array');
         Parser::parse(['a' => 'b']);
     }
 
-    public function testAssertsThatASourceToParseIsNotObject()
+    public function testAssertsThatASourceToParseIsNotObject() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage('GraphQL query body is expected to be string, but got stdClass');
@@ -57,7 +57,7 @@ fragment MissingOn Type
      * @dataProvider parseProvidesUsefulErrors
      * @see it('parse provides useful errors')
      */
-    public function testParseProvidesUsefulErrors($str, $expectedMessage, $stringRepresentation, $expectedPositions = null, $expectedLocations = null)
+    public function testParseProvidesUsefulErrors($str, $expectedMessage, $stringRepresentation, $expectedPositions = null, $expectedLocations = null) : void
     {
         try {
             Parser::parse($str);
@@ -79,7 +79,7 @@ fragment MissingOn Type
     /**
      * @see it('parse provides useful error when using source')
      */
-    public function testParseProvidesUsefulErrorWhenUsingSource()
+    public function testParseProvidesUsefulErrorWhenUsingSource() : void
     {
         try {
             Parser::parse(new Source('query', 'MyQuery.graphql'));
@@ -95,7 +95,7 @@ fragment MissingOn Type
     /**
      * @see it('parses variable inline values')
      */
-    public function testParsesVariableInlineValues()
+    public function testParsesVariableInlineValues() : void
     {
         $this->expectNotToPerformAssertions();
         // Following line should not throw:
@@ -105,7 +105,7 @@ fragment MissingOn Type
     /**
      * @see it('parses constant default values')
      */
-    public function testParsesConstantDefaultValues()
+    public function testParsesConstantDefaultValues() : void
     {
         $this->expectSyntaxError(
             'query Foo($x: Complex = { a: { b: [ $var ] } }) { field }',
@@ -117,7 +117,7 @@ fragment MissingOn Type
     /**
      * @see it('does not accept fragments spread of "on"')
      */
-    public function testDoesNotAcceptFragmentsNamedOn()
+    public function testDoesNotAcceptFragmentsNamedOn() : void
     {
         $this->expectSyntaxError(
             'fragment on on on { on }',
@@ -129,7 +129,7 @@ fragment MissingOn Type
     /**
      * @see it('does not accept fragments spread of "on"')
      */
-    public function testDoesNotAcceptFragmentSpreadOfOn()
+    public function testDoesNotAcceptFragmentSpreadOfOn() : void
     {
         $this->expectSyntaxError(
             '{ ...on }',
@@ -141,7 +141,7 @@ fragment MissingOn Type
     /**
      * @see it('parses multi-byte characters')
      */
-    public function testParsesMultiByteCharacters()
+    public function testParsesMultiByteCharacters() : void
     {
         // Note: \u0A0A could be naively interpretted as two line-feed chars.
 
@@ -176,7 +176,7 @@ HEREDOC;
     /**
      * @see it('parses kitchen sink')
      */
-    public function testParsesKitchenSink()
+    public function testParsesKitchenSink() : void
     {
         // Following should not throw:
         $kitchenSink = file_get_contents(__DIR__ . '/kitchen-sink.graphql');
@@ -187,7 +187,7 @@ HEREDOC;
     /**
      * allows non-keywords anywhere a Name is allowed
      */
-    public function testAllowsNonKeywordsAnywhereANameIsAllowed()
+    public function testAllowsNonKeywordsAnywhereANameIsAllowed() : void
     {
         $nonKeywords = [
             'on',
@@ -220,7 +220,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses anonymous mutation operations')
      */
-    public function testParsessAnonymousMutationOperations()
+    public function testParsessAnonymousMutationOperations() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw:
@@ -234,7 +234,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses anonymous subscription operations')
      */
-    public function testParsesAnonymousSubscriptionOperations()
+    public function testParsesAnonymousSubscriptionOperations() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw:
@@ -248,7 +248,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses named mutation operations')
      */
-    public function testParsesNamedMutationOperations()
+    public function testParsesNamedMutationOperations() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw:
@@ -262,7 +262,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses named subscription operations')
      */
-    public function testParsesNamedSubscriptionOperations()
+    public function testParsesNamedSubscriptionOperations() : void
     {
         $this->expectNotToPerformAssertions();
         Parser::parse('
@@ -275,7 +275,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('creates ast')
      */
-    public function testParseCreatesAst()
+    public function testParseCreatesAst() : void
     {
         $source = new Source('{
   node(id: 4) {
@@ -379,7 +379,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('creates ast from nameless query without variables')
      */
-    public function testParseCreatesAstFromNamelessQueryWithoutVariables()
+    public function testParseCreatesAstFromNamelessQueryWithoutVariables() : void
     {
         $source = new Source('query {
   node {
@@ -454,7 +454,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('allows parsing without source location information')
      */
-    public function testAllowsParsingWithoutSourceLocationInformation()
+    public function testAllowsParsingWithoutSourceLocationInformation() : void
     {
         $source = new Source('{ id }');
         $result = Parser::parse($source, ['noLocation' => true]);
@@ -465,7 +465,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('Experimental: allows parsing fragment defined variables')
      */
-    public function testExperimentalAllowsParsingFragmentDefinedVariables()
+    public function testExperimentalAllowsParsingFragmentDefinedVariables() : void
     {
         $source = new Source('fragment a($v: Boolean = false) on t { f(v: $v) }');
         // not throw
@@ -478,7 +478,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('contains location information that only stringifys start/end')
      */
-    public function testContainsLocationInformationThatOnlyStringifysStartEnd()
+    public function testContainsLocationInformationThatOnlyStringifysStartEnd() : void
     {
         $source = new Source('{ id }');
         $result = Parser::parse($source);
@@ -488,7 +488,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('contains references to source')
      */
-    public function testContainsReferencesToSource()
+    public function testContainsReferencesToSource() : void
     {
         $source = new Source('{ id }');
         $result = Parser::parse($source);
@@ -498,7 +498,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('contains references to start and end tokens')
      */
-    public function testContainsReferencesToStartAndEndTokens()
+    public function testContainsReferencesToStartAndEndTokens() : void
     {
         $source = new Source('{ id }');
         $result = Parser::parse($source);
@@ -511,7 +511,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses null value')
      */
-    public function testParsesNullValues()
+    public function testParsesNullValues() : void
     {
         $this->assertEquals([
             'kind' => NodeKind::NULL,
@@ -522,7 +522,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses list values')
      */
-    public function testParsesListValues()
+    public function testParsesListValues() : void
     {
         $this->assertEquals([
             'kind' => NodeKind::LST,
@@ -548,7 +548,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses well known types')
      */
-    public function testParsesWellKnownTypes()
+    public function testParsesWellKnownTypes() : void
     {
         $this->assertEquals([
             'kind' => NodeKind::NAMED_TYPE,
@@ -564,7 +564,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses custom types')
      */
-    public function testParsesCustomTypes()
+    public function testParsesCustomTypes() : void
     {
         $this->assertEquals([
             'kind' => NodeKind::NAMED_TYPE,
@@ -580,7 +580,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses list types')
      */
-    public function testParsesListTypes()
+    public function testParsesListTypes() : void
     {
         $this->assertEquals([
             'kind' => NodeKind::LIST_TYPE,
@@ -600,7 +600,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses non-null types')
      */
-    public function testParsesNonNullTypes()
+    public function testParsesNonNullTypes() : void
     {
         $this->assertEquals([
             'kind' => NodeKind::NON_NULL_TYPE,
@@ -620,7 +620,7 @@ fragment $fragmentName on Type {
     /**
      * @see it('parses nested types')
      */
-    public function testParsesNestedTypes()
+    public function testParsesNestedTypes() : void
     {
         $this->assertEquals([
             'kind' => NodeKind::LIST_TYPE,
diff --git a/tests/Language/PrinterTest.php b/tests/Language/PrinterTest.php
index f5d82ef..cba6b11 100644
--- a/tests/Language/PrinterTest.php
+++ b/tests/Language/PrinterTest.php
@@ -19,7 +19,7 @@ class PrinterTest extends TestCase
     /**
      * @see it('does not alter ast')
      */
-    public function testDoesntAlterAST()
+    public function testDoesntAlterAST() : void
     {
         $kitchenSink = file_get_contents(__DIR__ . '/kitchen-sink.graphql');
         $ast = Parser::parse($kitchenSink);
@@ -34,7 +34,7 @@ class PrinterTest extends TestCase
     /**
      * @see it('prints minimal ast')
      */
-    public function testPrintsMinimalAst()
+    public function testPrintsMinimalAst() : void
     {
         $ast = new FieldNode(['name' => new NameNode(['value' => 'foo'])]);
         $this->assertEquals('foo', Printer::doPrint($ast));
@@ -43,7 +43,7 @@ class PrinterTest extends TestCase
     /**
      * @see it('produces helpful error messages')
      */
-    public function testProducesHelpfulErrorMessages()
+    public function testProducesHelpfulErrorMessages() : void
     {
         $badAst1 = new \ArrayObject(['random' => 'Data']);
         $this->expectException(\Throwable::class);
@@ -54,7 +54,7 @@ class PrinterTest extends TestCase
     /**
      * @see it('correctly prints non-query operations without name')
      */
-    public function testCorrectlyPrintsOpsWithoutName()
+    public function testCorrectlyPrintsOpsWithoutName() : void
     {
         $queryAstShorthanded = Parser::parse('query { id, name }');
 
@@ -97,7 +97,7 @@ class PrinterTest extends TestCase
     /**
      * @see it('correctly prints single-line with leading space')
      */
-    public function testCorrectlyPrintsSingleLineBlockStringsWithLeadingSpace()
+    public function testCorrectlyPrintsSingleLineBlockStringsWithLeadingSpace() : void
     {
         $mutationAstWithArtifacts = Parser::parse(
           '{ field(arg: """    space-led value""") }'
@@ -112,7 +112,7 @@ class PrinterTest extends TestCase
     /**
      * @see it('correctly prints string with a first line indentation')
      */
-    public function testCorrectlyPrintsBlockStringsWithAFirstLineIndentation()
+    public function testCorrectlyPrintsBlockStringsWithAFirstLineIndentation() : void
     {
         $mutationAstWithArtifacts = Parser::parse(
             '{
@@ -137,7 +137,7 @@ class PrinterTest extends TestCase
     /**
      * @see it('correctly prints single-line with leading space and quotation')
      */
-    public function testCorrectlyPrintsSingleLineWithLeadingSpaceAndQuotation()
+    public function testCorrectlyPrintsSingleLineWithLeadingSpaceAndQuotation() : void
     {
         $mutationAstWithArtifacts = Parser::parse('
             {
@@ -158,7 +158,7 @@ END;
     /**
      * @see it('Experimental: correctly prints fragment defined variables')
      */
-    public function testExperimentalCorrectlyPrintsFragmentDefinedVariables()
+    public function testExperimentalCorrectlyPrintsFragmentDefinedVariables() : void
     {
         $fragmentWithVariable = Parser::parse('
           fragment Foo($a: ComplexType, $b: Boolean = false) on TestType {
@@ -180,7 +180,7 @@ END;
     /**
      * @see it('correctly prints single-line with leading space and quotation')
      */
-    public function testCorrectlyPrintsSingleLineStringsWithLeadingSpaceAndQuotation()
+    public function testCorrectlyPrintsSingleLineStringsWithLeadingSpaceAndQuotation() : void
     {
         $mutationAstWithArtifacts = Parser::parse(
             '{
@@ -199,7 +199,7 @@ END;
     /**
      * @see it('prints kitchen sink')
      */
-    public function testPrintsKitchenSink()
+    public function testPrintsKitchenSink() : void
     {
         $kitchenSink = file_get_contents(__DIR__ . '/kitchen-sink.graphql');
         $ast = Parser::parse($kitchenSink);
diff --git a/tests/Language/SchemaParserTest.php b/tests/Language/SchemaParserTest.php
index b44ce5c..465cf27 100644
--- a/tests/Language/SchemaParserTest.php
+++ b/tests/Language/SchemaParserTest.php
@@ -14,7 +14,7 @@ class SchemaParserTest extends TestCase
     /**
      * @see it('Simple type')
      */
-    public function testSimpleType()
+    public function testSimpleType() : void
     {
         $body = '
 type Hello {
@@ -50,7 +50,7 @@ type Hello {
     /**
      * @see it('parses type with description string')
      */
-    public function testParsesTypeWithDescriptionString()
+    public function testParsesTypeWithDescriptionString() : void
     {
         $body = '
 "Description"
@@ -92,7 +92,7 @@ type Hello {
     /**
      * @see it('parses type with description multi-linestring')
      */
-    public function testParsesTypeWithDescriptionMultiLineString()
+    public function testParsesTypeWithDescriptionMultiLineString() : void
     {
         $body = '
 """
@@ -137,7 +137,7 @@ type Hello {
     /**
      * @see it('Simple extension')
      */
-    public function testSimpleExtension()
+    public function testSimpleExtension() : void
     {
         $body = '
 extend type Hello {
@@ -174,7 +174,7 @@ extend type Hello {
     /**
      * @see it('Extension without fields')
      */
-    public function testExtensionWithoutFields()
+    public function testExtensionWithoutFields() : void
     {
         $body = 'extend type Hello implements Greeting';
         $doc = Parser::parse($body);
@@ -203,7 +203,7 @@ extend type Hello {
     /**
      * @see it('Extension without fields followed by extension')
      */
-    public function testExtensionWithoutFieldsFollowedByExtension()
+    public function testExtensionWithoutFieldsFollowedByExtension() : void
     {
         $body = '
           extend type Hello implements Greeting
@@ -239,7 +239,7 @@ extend type Hello {
     /**
      * @see it('Extension without anything throws')
      */
-    public function testExtensionWithoutAnythingThrows()
+    public function testExtensionWithoutAnythingThrows() : void
     {
         $this->expectSyntaxError(
             'extend type Hello',
@@ -251,7 +251,7 @@ extend type Hello {
     /**
      * @see it('Extension do not include descriptions')
      */
-    public function testExtensionDoNotIncludeDescriptions()
+    public function testExtensionDoNotIncludeDescriptions() : void
     {
         $body = '
       "Description"
@@ -268,7 +268,7 @@ extend type Hello {
     /**
      * @see it('Extension do not include descriptions')
      */
-    public function testExtensionDoNotIncludeDescriptions2()
+    public function testExtensionDoNotIncludeDescriptions2() : void
     {
         $body = '
       extend "Description" type Hello {
@@ -285,7 +285,7 @@ extend type Hello {
     /**
      * @see it('Simple non-null type')
      */
-    public function testSimpleNonNullType()
+    public function testSimpleNonNullType() : void
     {
         $body = '
 type Hello {
@@ -328,7 +328,7 @@ type Hello {
     /**
      * @see it('Simple type inheriting interface')
      */
-    public function testSimpleTypeInheritingInterface()
+    public function testSimpleTypeInheritingInterface() : void
     {
         $body = 'type Hello implements World { field: String }';
         $loc = function($start, $end) { return TestUtils::locArray($start, $end); };
@@ -364,7 +364,7 @@ type Hello {
     /**
      * @see it('Simple type inheriting multiple interfaces')
      */
-    public function testSimpleTypeInheritingMultipleInterfaces()
+    public function testSimpleTypeInheritingMultipleInterfaces() : void
     {
         $body = 'type Hello implements Wo & rld { field: String }';
         $loc = function($start, $end) {return TestUtils::locArray($start, $end);};
@@ -401,7 +401,7 @@ type Hello {
     /**
      * @see it('Simple type inheriting multiple interfaces with leading ampersand')
      */
-    public function testSimpleTypeInheritingMultipleInterfacesWithLeadingAmpersand()
+    public function testSimpleTypeInheritingMultipleInterfacesWithLeadingAmpersand() : void
     {
         $body = 'type Hello implements & Wo & rld { field: String }';
         $loc = function($start, $end) {return TestUtils::locArray($start, $end);};
@@ -436,7 +436,7 @@ type Hello {
     /**
      * @see it('Single value enum')
      */
-    public function testSingleValueEnum()
+    public function testSingleValueEnum() : void
     {
         $body = 'enum Hello { WORLD }';
         $loc = function($start, $end) {return TestUtils::locArray($start, $end);};
@@ -463,7 +463,7 @@ type Hello {
     /**
      * @see it('Double value enum')
      */
-    public function testDoubleValueEnum()
+    public function testDoubleValueEnum() : void
     {
         $body = 'enum Hello { WO, RLD }';
         $loc = function($start, $end) {return TestUtils::locArray($start, $end);};
@@ -493,7 +493,7 @@ type Hello {
     /**
      * @see it('Simple interface')
      */
-    public function testSimpleInterface()
+    public function testSimpleInterface() : void
     {
         $body = '
 interface Hello {
@@ -528,7 +528,7 @@ interface Hello {
     /**
      * @see it('Simple field with arg')
      */
-    public function testSimpleFieldWithArg()
+    public function testSimpleFieldWithArg() : void
     {
         $body = '
 type Hello {
@@ -573,7 +573,7 @@ type Hello {
     /**
      * @see it('Simple field with arg with default value')
      */
-    public function testSimpleFieldWithArgWithDefaultValue()
+    public function testSimpleFieldWithArgWithDefaultValue() : void
     {
         $body = '
 type Hello {
@@ -617,7 +617,7 @@ type Hello {
     /**
      * @see it('Simple field with list arg')
      */
-    public function testSimpleFieldWithListArg()
+    public function testSimpleFieldWithListArg() : void
     {
         $body = '
 type Hello {
@@ -662,7 +662,7 @@ type Hello {
     /**
      * @see it('Simple field with two args')
      */
-    public function testSimpleFieldWithTwoArgs()
+    public function testSimpleFieldWithTwoArgs() : void
     {
         $body = '
 type Hello {
@@ -713,7 +713,7 @@ type Hello {
     /**
      * @see it('Simple union')
      */
-    public function testSimpleUnion()
+    public function testSimpleUnion() : void
     {
         $body = 'union Hello = World';
         $doc = Parser::parse($body);
@@ -739,7 +739,7 @@ type Hello {
     /**
      * @see it('Union with two types')
      */
-    public function testUnionWithTwoTypes()
+    public function testUnionWithTwoTypes() : void
     {
         $body = 'union Hello = Wo | Rld';
         $doc = Parser::parse($body);
@@ -769,7 +769,7 @@ type Hello {
     /**
      * @see it('Union with two types and leading pipe')
      */
-    public function testUnionWithTwoTypesAndLeadingPipe()
+    public function testUnionWithTwoTypesAndLeadingPipe() : void
     {
         $body = 'union Hello = | Wo | Rld';
         $doc = Parser::parse($body);
@@ -796,7 +796,7 @@ type Hello {
     /**
      * @see it('Union fails with no types')
      */
-    public function testUnionFailsWithNoTypes()
+    public function testUnionFailsWithNoTypes() : void
     {
         $this->expectSyntaxError(
             'union Hello = |',
@@ -808,7 +808,7 @@ type Hello {
     /**
      * @see it('Union fails with leading douple pipe')
      */
-    public function testUnionFailsWithLeadingDoublePipe()
+    public function testUnionFailsWithLeadingDoublePipe() : void
     {
         $this->expectSyntaxError(
             'union Hello = || Wo | Rld',
@@ -820,7 +820,7 @@ type Hello {
     /**
      * @see it('Union fails with double pipe')
      */
-    public function testUnionFailsWithDoublePipe()
+    public function testUnionFailsWithDoublePipe() : void
     {
         $this->expectSyntaxError(
             'union Hello = Wo || Rld',
@@ -832,7 +832,7 @@ type Hello {
     /**
      * @see it('Union fails with trailing pipe')
      */
-    public function testUnionFailsWithTrailingPipe()
+    public function testUnionFailsWithTrailingPipe() : void
     {
         $this->expectSyntaxError(
             'union Hello = | Wo | Rld |',
@@ -844,7 +844,7 @@ type Hello {
     /**
      * @see it('Scalar')
      */
-    public function testScalar()
+    public function testScalar() : void
     {
         $body = 'scalar Hello';
         $doc = Parser::parse($body);
@@ -868,7 +868,7 @@ type Hello {
     /**
      * @see it('Simple input object')
      */
-    public function testSimpleInputObject()
+    public function testSimpleInputObject() : void
     {
         $body = '
 input Hello {
@@ -904,7 +904,7 @@ input Hello {
     /**
      * @see it('Simple input object with args should fail')
      */
-    public function testSimpleInputObjectWithArgsShouldFail()
+    public function testSimpleInputObjectWithArgsShouldFail() : void
     {
         $body = '
       input Hello {
@@ -920,7 +920,7 @@ input Hello {
     /**
      * @see it('Directive with incorrect locations')
      */
-    public function testDirectiveWithIncorrectLocationShouldFail()
+    public function testDirectiveWithIncorrectLocationShouldFail() : void
     {
         $body = '
       directive @foo on FIELD | INCORRECT_LOCATION
@@ -932,7 +932,7 @@ input Hello {
         );
     }
 
-    public function testDoesNotAllowEmptyFields()
+    public function testDoesNotAllowEmptyFields() : void
     {
         $body = 'type Hello { }';
         $this->expectSyntaxError($body, 'Syntax Error: Expected Name, found }', new SourceLocation(1, 14));
@@ -941,7 +941,7 @@ input Hello {
     /**
      * @see it('Option: allowLegacySDLEmptyFields supports type with empty fields')
      */
-    public function testAllowLegacySDLEmptyFieldsOption()
+    public function testAllowLegacySDLEmptyFieldsOption() : void
     {
         $body = 'type Hello { }';
         $doc = Parser::parse($body, ['allowLegacySDLEmptyFields' => true]);
@@ -955,7 +955,7 @@ input Hello {
         $this->assertArraySubset($expected, $doc->toArray(true));
     }
 
-    public function testDoesntAllowLegacySDLImplementsInterfacesByDefault()
+    public function testDoesntAllowLegacySDLImplementsInterfacesByDefault() : void
     {
         $body = 'type Hello implements Wo rld { field: String }';
         $this->expectSyntaxError($body, 'Syntax Error: Unexpected Name "rld"', new SourceLocation(1, 26));
@@ -964,7 +964,7 @@ input Hello {
     /**
      * @see it('Option: allowLegacySDLImplementsInterfaces')
      */
-    public function testDefaultSDLImplementsInterfaces()
+    public function testDefaultSDLImplementsInterfaces() : void
     {
         $body = 'type Hello implements Wo rld { field: String }';
         $doc = Parser::parse($body, ['allowLegacySDLImplementsInterfaces' => true]);
diff --git a/tests/Language/SchemaPrinterTest.php b/tests/Language/SchemaPrinterTest.php
index 8b30087..b0cc05f 100644
--- a/tests/Language/SchemaPrinterTest.php
+++ b/tests/Language/SchemaPrinterTest.php
@@ -13,7 +13,7 @@ class SchemaPrinterTest extends TestCase
     /**
      * @see it('prints minimal ast')
      */
-    public function testPrintsMinimalAst()
+    public function testPrintsMinimalAst() : void
     {
         $ast = new ScalarTypeDefinitionNode([
             'name' => new NameNode(['value' => 'foo'])
@@ -24,7 +24,7 @@ class SchemaPrinterTest extends TestCase
     /**
      * @see it('produces helpful error messages')
      */
-    public function testProducesHelpfulErrorMessages()
+    public function testProducesHelpfulErrorMessages() : void
     {
         $this->expectException(Throwable::class);
         $this->expectExceptionMessage('Invalid AST Node: {"random":"Data"}');
@@ -37,7 +37,7 @@ class SchemaPrinterTest extends TestCase
     /**
      * @see it('does not alter ast')
      */
-    public function testDoesNotAlterAst()
+    public function testDoesNotAlterAst() : void
     {
         $kitchenSink = file_get_contents(__DIR__ . '/schema-kitchen-sink.graphql');
 
@@ -48,7 +48,7 @@ class SchemaPrinterTest extends TestCase
         $this->assertEquals($astCopy, $ast);
     }
 
-    public function testPrintsKitchenSink()
+    public function testPrintsKitchenSink() : void
     {
         $kitchenSink = file_get_contents(__DIR__ . '/schema-kitchen-sink.graphql');
 
diff --git a/tests/Language/SerializationTest.php b/tests/Language/SerializationTest.php
index f2fe16c..7624fdc 100644
--- a/tests/Language/SerializationTest.php
+++ b/tests/Language/SerializationTest.php
@@ -10,7 +10,7 @@ use PHPUnit\Framework\TestCase;
 
 class SerializationTest extends TestCase
 {
-    public function testSerializesAst()
+    public function testSerializesAst() : void
     {
         $kitchenSink = file_get_contents(__DIR__ . '/kitchen-sink.graphql');
         $ast = Parser::parse($kitchenSink);
@@ -18,7 +18,7 @@ class SerializationTest extends TestCase
         $this->assertEquals($expectedAst, $ast->toArray(true));
     }
 
-    public function testUnserializesAst()
+    public function testUnserializesAst() : void
     {
         $kitchenSink = file_get_contents(__DIR__ . '/kitchen-sink.graphql');
         $serializedAst = json_decode(file_get_contents(__DIR__ . '/kitchen-sink.ast'), true);
@@ -27,7 +27,7 @@ class SerializationTest extends TestCase
         $this->assertNodesAreEqual($parsedAst, $actualAst);
     }
 
-    public function testSerializeSupportsNoLocationOption()
+    public function testSerializeSupportsNoLocationOption() : void
     {
         $kitchenSink = file_get_contents(__DIR__ . '/kitchen-sink.graphql');
         $ast = Parser::parse($kitchenSink, ['noLocation' => true]);
@@ -35,7 +35,7 @@ class SerializationTest extends TestCase
         $this->assertEquals($expectedAst, $ast->toArray(true));
     }
 
-    public function testUnserializeSupportsNoLocationOption()
+    public function testUnserializeSupportsNoLocationOption() : void
     {
         $kitchenSink = file_get_contents(__DIR__ . '/kitchen-sink.graphql');
         $serializedAst = json_decode(file_get_contents(__DIR__ . '/kitchen-sink-noloc.ast'), true);
diff --git a/tests/Language/TokenTest.php b/tests/Language/TokenTest.php
index 541a618..ea21d20 100644
--- a/tests/Language/TokenTest.php
+++ b/tests/Language/TokenTest.php
@@ -6,7 +6,7 @@ use PHPUnit\Framework\TestCase;
 
 class TokenTest extends TestCase
 {
-    public function testReturnTokenOnArray()
+    public function testReturnTokenOnArray() : void
     {
         $token = new Token('Kind', 1, 10, 3, 5);
         $expected = [
diff --git a/tests/Language/VisitorTest.php b/tests/Language/VisitorTest.php
index fd7bb20..300dea8 100644
--- a/tests/Language/VisitorTest.php
+++ b/tests/Language/VisitorTest.php
@@ -84,7 +84,7 @@ class VisitorTest extends ValidatorTestCase
         }
     }
 
-    public function testValidatesPathArgument()
+    public function testValidatesPathArgument() : void
     {
         $visited = [];
 
@@ -117,7 +117,7 @@ class VisitorTest extends ValidatorTestCase
         $this->assertEquals($expected, $visited);
     }
 
-    public function testAllowsEditingNodeOnEnterAndOnLeave()
+    public function testAllowsEditingNodeOnEnterAndOnLeave() : void
     {
         $ast = Parser::parse('{ a, b, c { a, b, c } }', [ 'noLocation' => true ]);
 
@@ -154,7 +154,7 @@ class VisitorTest extends ValidatorTestCase
         $this->assertEquals($expected, $editedAst);
     }
 
-    public function testAllowsEditingRootNodeOnEnterAndLeave()
+    public function testAllowsEditingRootNodeOnEnterAndLeave() : void
     {
         $ast         = Parser::parse('{ a, b, c { a, b, c } }', [ 'noLocation' => true ]);
         $definitions = $ast->definitions;
@@ -185,7 +185,7 @@ class VisitorTest extends ValidatorTestCase
         $this->assertEquals($tmp, $editedAst);
     }
 
-    public function testAllowsForEditingOnEnter()
+    public function testAllowsForEditingOnEnter() : void
     {
         $ast       = Parser::parse('{ a, b, c { a, b, c } }', ['noLocation' => true]);
         $editedAst = Visitor::visit($ast, [
@@ -207,7 +207,7 @@ class VisitorTest extends ValidatorTestCase
         );
     }
 
-    public function testAllowsForEditingOnLeave()
+    public function testAllowsForEditingOnLeave() : void
     {
         $ast       = Parser::parse('{ a, b, c { a, b, c } }', ['noLocation' => true]);
         $editedAst = Visitor::visit($ast, [
@@ -230,7 +230,7 @@ class VisitorTest extends ValidatorTestCase
         );
     }
 
-    public function testVisitsEditedNode()
+    public function testVisitsEditedNode() : void
     {
         $addedField = new FieldNode([
             'name' => new NameNode(['value' => '__typename']),
@@ -261,7 +261,7 @@ class VisitorTest extends ValidatorTestCase
         $this->assertTrue($didVisitAddedField);
     }
 
-    public function testAllowsSkippingASubTree()
+    public function testAllowsSkippingASubTree() : void
     {
         $visited = [];
         $ast     = Parser::parse('{ a, b { x }, c }', ['noLocation' => true]);
@@ -301,7 +301,7 @@ class VisitorTest extends ValidatorTestCase
         $this->assertEquals($expected, $visited);
     }
 
-    public function testAllowsEarlyExitWhileVisiting()
+    public function testAllowsEarlyExitWhileVisiting() : void
     {
         $visited = [];
         $ast     = Parser::parse('{ a, b { x }, c }', ['noLocation' => true]);
@@ -339,7 +339,7 @@ class VisitorTest extends ValidatorTestCase
         $this->assertEquals($expected, $visited);
     }
 
-    public function testAllowsEarlyExitWhileLeaving()
+    public function testAllowsEarlyExitWhileLeaving() : void
     {
         $visited = [];
 
@@ -377,7 +377,7 @@ class VisitorTest extends ValidatorTestCase
         ]);
     }
 
-    public function testAllowsANamedFunctionsVisitorAPI()
+    public function testAllowsANamedFunctionsVisitorAPI() : void
     {
         $visited = [];
         $ast     = Parser::parse('{ a, b { x }, c }', ['noLocation' => true]);
@@ -413,7 +413,7 @@ class VisitorTest extends ValidatorTestCase
         $this->assertEquals($expected, $visited);
     }
 
-    public function testExperimentalVisitsVariablesDefinedInFragments()
+    public function testExperimentalVisitsVariablesDefinedInFragments() : void
     {
         $ast     = Parser::parse(
             'fragment a($v: Boolean = false) on t { f }',
@@ -469,7 +469,7 @@ class VisitorTest extends ValidatorTestCase
         $this->assertEquals($expected, $visited);
     }
 
-    public function testVisitsKitchenSink()
+    public function testVisitsKitchenSink() : void
     {
         $kitchenSink = file_get_contents(__DIR__ . '/kitchen-sink.graphql');
         $ast         = Parser::parse($kitchenSink);
@@ -808,7 +808,7 @@ class VisitorTest extends ValidatorTestCase
      * Describe: visitInParallel
      * Note: nearly identical to the above test of the same test but using visitInParallel.
      */
-    public function testAllowsSkippingSubTree()
+    public function testAllowsSkippingSubTree() : void
     {
         $visited = [];
 
@@ -850,7 +850,7 @@ class VisitorTest extends ValidatorTestCase
         ], $visited);
     }
 
-    public function testAllowsSkippingDifferentSubTrees()
+    public function testAllowsSkippingDifferentSubTrees() : void
     {
         $visited = [];
 
@@ -922,7 +922,7 @@ class VisitorTest extends ValidatorTestCase
         ], $visited);
     }
 
-    public function testAllowsEarlyExitWhileVisiting2()
+    public function testAllowsEarlyExitWhileVisiting2() : void
     {
         $visited = [];
 
@@ -960,7 +960,7 @@ class VisitorTest extends ValidatorTestCase
         ], $visited);
     }
 
-    public function testAllowsEarlyExitFromDifferentPoints()
+    public function testAllowsEarlyExitFromDifferentPoints() : void
     {
         $visited = [];
 
@@ -1020,7 +1020,7 @@ class VisitorTest extends ValidatorTestCase
         ], $visited);
     }
 
-    public function testAllowsEarlyExitWhileLeaving2()
+    public function testAllowsEarlyExitWhileLeaving2() : void
     {
         $visited = [];
 
@@ -1059,7 +1059,7 @@ class VisitorTest extends ValidatorTestCase
         ], $visited);
     }
 
-    public function testAllowsEarlyExitFromLeavingDifferentPoints()
+    public function testAllowsEarlyExitFromLeavingDifferentPoints() : void
     {
         $visited = [];
 
@@ -1133,7 +1133,7 @@ class VisitorTest extends ValidatorTestCase
         ], $visited);
     }
 
-    public function testAllowsForEditingOnEnter2()
+    public function testAllowsForEditingOnEnter2() : void
     {
         $visited = [];
 
@@ -1197,7 +1197,7 @@ class VisitorTest extends ValidatorTestCase
         ], $visited);
     }
 
-    public function testAllowsForEditingOnLeave2()
+    public function testAllowsForEditingOnLeave2() : void
     {
         $visited = [];
 
@@ -1271,7 +1271,7 @@ class VisitorTest extends ValidatorTestCase
     /**
      * Describe: visitWithTypeInfo
      */
-    public function testMaintainsTypeInfoDuringVisit()
+    public function testMaintainsTypeInfoDuringVisit() : void
     {
         $visited = [];
 
@@ -1353,7 +1353,7 @@ class VisitorTest extends ValidatorTestCase
         ], $visited);
     }
 
-    public function testMaintainsTypeInfoDuringEdit()
+    public function testMaintainsTypeInfoDuringEdit() : void
     {
         $visited  = [];
         $typeInfo = new TypeInfo(ValidatorTestCase::getTestSchema());
diff --git a/tests/Server/PsrResponseTest.php b/tests/Server/PsrResponseTest.php
index 9988d55..b3ff6ec 100644
--- a/tests/Server/PsrResponseTest.php
+++ b/tests/Server/PsrResponseTest.php
@@ -9,7 +9,7 @@ use PHPUnit\Framework\TestCase;
 
 class PsrResponseTest extends TestCase
 {
-    public function testConvertsResultToPsrResponse()
+    public function testConvertsResultToPsrResponse() : void
     {
         $result = new ExecutionResult(['key' => 'value']);
         $stream = new PsrStreamStub();
diff --git a/tests/Server/QueryExecutionTest.php b/tests/Server/QueryExecutionTest.php
index 1381eda..0b7d473 100644
--- a/tests/Server/QueryExecutionTest.php
+++ b/tests/Server/QueryExecutionTest.php
@@ -31,7 +31,7 @@ class QueryExecutionTest extends ServerTestCase
             ->setSchema($schema);
     }
 
-    public function testSimpleQueryExecution()
+    public function testSimpleQueryExecution() : void
     {
         $query = '{f1}';
 
@@ -44,7 +44,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertQueryResultEquals($expected, $query);
     }
 
-    public function testReturnsSyntaxErrors()
+    public function testReturnsSyntaxErrors() : void
     {
         $query = '{f1';
 
@@ -57,7 +57,7 @@ class QueryExecutionTest extends ServerTestCase
         );
     }
 
-    public function testDebugExceptions()
+    public function testDebugExceptions() : void
     {
         $debug = Debug::INCLUDE_DEBUG_MESSAGE | Debug::INCLUDE_TRACE;
         $this->config->setDebug($debug);
@@ -87,7 +87,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertArraySubset($expected, $result);
     }
 
-    public function testPassesRootValueAndContext()
+    public function testPassesRootValueAndContext() : void
     {
         $rootValue = 'myRootValue';
         $context = new \stdClass();
@@ -107,7 +107,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertSame($rootValue, $context->testedRootValue);
     }
 
-    public function testPassesVariables()
+    public function testPassesVariables() : void
     {
         $variables = ['a' => 'a', 'b' => 'b'];
         $query = '
@@ -125,7 +125,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertQueryResultEquals($expected, $query, $variables);
     }
 
-    public function testPassesCustomValidationRules()
+    public function testPassesCustomValidationRules() : void
     {
         $query = '
             {nonExistentField}
@@ -155,7 +155,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertTrue($called);
     }
 
-    public function testAllowsValidationRulesAsClosure()
+    public function testAllowsValidationRulesAsClosure() : void
     {
         $called = false;
         $params = $doc = $operationType = null;
@@ -176,7 +176,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertEquals('query', $operationType);
     }
 
-    public function testAllowsDifferentValidationRulesDependingOnOperation()
+    public function testAllowsDifferentValidationRulesDependingOnOperation() : void
     {
         $q1 = '{f1}';
         $q2 = '{invalid}';
@@ -210,7 +210,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertTrue($called2);
     }
 
-    public function testAllowsSkippingValidation()
+    public function testAllowsSkippingValidation() : void
     {
         $this->config->setValidationRules([]);
         $query = '{nonExistentField}';
@@ -218,7 +218,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertQueryResultEquals($expected, $query);
     }
 
-    public function testPersistedQueriesAreDisabledByDefault()
+    public function testPersistedQueriesAreDisabledByDefault() : void
     {
         $result = $this->executePersistedQuery('some-id');
 
@@ -233,7 +233,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertEquals($expected, $result->toArray());
     }
 
-    public function testBatchedQueriesAreDisabledByDefault()
+    public function testBatchedQueriesAreDisabledByDefault() : void
     {
         $batch = [
             [
@@ -269,7 +269,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertEquals($expected[1], $result[1]->toArray());
     }
 
-    public function testMutationsAreNotAllowedInReadonlyMode()
+    public function testMutationsAreNotAllowedInReadonlyMode() : void
     {
         $mutation = 'mutation { a }';
 
@@ -286,7 +286,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertEquals($expected, $result->toArray());
     }
 
-    public function testAllowsPersistentQueries()
+    public function testAllowsPersistentQueries() : void
     {
         $called = false;
         $this->config->setPersistentQueryLoader(function($queryId, OperationParams $params) use (&$called) {
@@ -317,7 +317,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertEquals($expected, $result->toArray());
     }
 
-    public function testProhibitsInvalidPersistedQueryLoader()
+    public function testProhibitsInvalidPersistedQueryLoader() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -330,7 +330,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->executePersistedQuery('some-id');
     }
 
-    public function testPersistedQueriesAreStillValidatedByDefault()
+    public function testPersistedQueriesAreStillValidatedByDefault() : void
     {
         $this->config->setPersistentQueryLoader(function() {
             return '{invalid}';
@@ -349,7 +349,7 @@ class QueryExecutionTest extends ServerTestCase
 
     }
 
-    public function testAllowSkippingValidationForPersistedQueries()
+    public function testAllowSkippingValidationForPersistedQueries() : void
     {
         $this->config
             ->setPersistentQueryLoader(function($queryId) {
@@ -386,7 +386,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertEquals($expected, $result->toArray());
     }
 
-    public function testProhibitsUnexpectedValidationRules()
+    public function testProhibitsUnexpectedValidationRules() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage('Expecting validation rules to be array or callable returning array, but got: instance of stdClass');
@@ -396,7 +396,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->executeQuery('{f1}');
     }
 
-    public function testExecutesBatchedQueries()
+    public function testExecutesBatchedQueries() : void
     {
         $this->config->setQueryBatching(true);
 
@@ -446,7 +446,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertArraySubset($expected[2], $result[2]->toArray());
     }
 
-    public function testDeferredsAreSharedAmongAllBatchedQueries()
+    public function testDeferredsAreSharedAmongAllBatchedQueries() : void
     {
         $batch = [
             [
@@ -510,7 +510,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertEquals($expected[2], $result[2]->toArray());
     }
 
-    public function testValidatesParamsBeforeExecution()
+    public function testValidatesParamsBeforeExecution() : void
     {
         $op = OperationParams::create(['queryBad' => '{f1}']);
         $helper = new Helper();
@@ -531,7 +531,7 @@ class QueryExecutionTest extends ServerTestCase
         );
     }
 
-    public function testAllowsContextAsClosure()
+    public function testAllowsContextAsClosure() : void
     {
         $called = false;
         $params = $doc = $operationType = null;
@@ -551,7 +551,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertEquals('query', $operationType);
     }
 
-    public function testAllowsRootValueAsClosure()
+    public function testAllowsRootValueAsClosure() : void
     {
         $called = false;
         $params = $doc = $operationType = null;
@@ -571,7 +571,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertEquals('query', $operationType);
     }
 
-    public function testAppliesErrorFormatter()
+    public function testAppliesErrorFormatter() : void
     {
         $called = false;
         $error = null;
@@ -606,7 +606,7 @@ class QueryExecutionTest extends ServerTestCase
         $this->assertArraySubset($expected, $formatted);
     }
 
-    public function testAppliesErrorsHandler()
+    public function testAppliesErrorsHandler() : void
     {
         $called = false;
         $errors = null;
diff --git a/tests/Server/RequestParsingTest.php b/tests/Server/RequestParsingTest.php
index aca363d..47d715c 100644
--- a/tests/Server/RequestParsingTest.php
+++ b/tests/Server/RequestParsingTest.php
@@ -12,7 +12,7 @@ use PHPUnit\Framework\TestCase;
 
 class RequestParsingTest extends TestCase
 {
-    public function testParsesGraphqlRequest()
+    public function testParsesGraphqlRequest() : void
     {
         $query = '{my query}';
         $parsed = [
@@ -26,7 +26,7 @@ class RequestParsingTest extends TestCase
         }
     }
 
-    public function testParsesUrlencodedRequest()
+    public function testParsesUrlencodedRequest() : void
     {
         $query = '{my query}';
         $variables = ['test' => 1, 'test2' => 2];
@@ -48,7 +48,7 @@ class RequestParsingTest extends TestCase
         }
     }
 
-    public function testParsesGetRequest()
+    public function testParsesGetRequest() : void
     {
         $query = '{my query}';
         $variables = ['test' => 1, 'test2' => 2];
@@ -70,7 +70,7 @@ class RequestParsingTest extends TestCase
         }
     }
 
-    public function testParsesMultipartFormdataRequest()
+    public function testParsesMultipartFormdataRequest() : void
     {
         $query = '{my query}';
         $variables = ['test' => 1, 'test2' => 2];
@@ -92,7 +92,7 @@ class RequestParsingTest extends TestCase
         }
     }
 
-    public function testParsesJSONRequest()
+    public function testParsesJSONRequest() : void
     {
         $query = '{my query}';
         $variables = ['test' => 1, 'test2' => 2];
@@ -113,7 +113,7 @@ class RequestParsingTest extends TestCase
         }
     }
 
-    public function testParsesVariablesAsJSON()
+    public function testParsesVariablesAsJSON() : void
     {
         $query = '{my query}';
         $variables = ['test' => 1, 'test2' => 2];
@@ -134,7 +134,7 @@ class RequestParsingTest extends TestCase
         }
     }
 
-    public function testIgnoresInvalidVariablesJson()
+    public function testIgnoresInvalidVariablesJson() : void
     {
         $query = '{my query}';
         $variables = '"some invalid json';
@@ -155,7 +155,7 @@ class RequestParsingTest extends TestCase
         }
     }
 
-    public function testParsesBatchJSONRequest()
+    public function testParsesBatchJSONRequest() : void
     {
         $body = [
             [
@@ -181,7 +181,7 @@ class RequestParsingTest extends TestCase
         }
     }
 
-    public function testFailsParsingInvalidRawJsonRequestRaw()
+    public function testFailsParsingInvalidRawJsonRequestRaw() : void
     {
         $body = 'not really{} a json';
 
@@ -190,7 +190,7 @@ class RequestParsingTest extends TestCase
             $this->parseRawRequest('application/json', $body);
         }
 
-    public function testFailsParsingInvalidRawJsonRequestPsr()
+    public function testFailsParsingInvalidRawJsonRequestPsr() : void
     {
         $body = 'not really{} a json';
 
@@ -199,7 +199,7 @@ class RequestParsingTest extends TestCase
             $this->parsePsrRequest('application/json', $body);
     }
 
-    public function testFailsParsingNonPreParsedPsrRequest()
+    public function testFailsParsingNonPreParsedPsrRequest() : void
     {
         try {
             $this->parsePsrRequest('application/json', json_encode(null));
@@ -213,9 +213,10 @@ class RequestParsingTest extends TestCase
         }
     }
 
-    // There is no equivalent for psr request, because it should throw
-
-    public function testFailsParsingNonArrayOrObjectJsonRequestRaw()
+    /**
+     * There is no equivalent for psr request, because it should throw
+     */
+    public function testFailsParsingNonArrayOrObjectJsonRequestRaw() : void
     {
         $body = '"str"';
 
@@ -224,7 +225,7 @@ class RequestParsingTest extends TestCase
             $this->parseRawRequest('application/json', $body);
         }
 
-    public function testFailsParsingNonArrayOrObjectJsonRequestPsr()
+    public function testFailsParsingNonArrayOrObjectJsonRequestPsr() : void
     {
         $body = '"str"';
 
@@ -233,7 +234,7 @@ class RequestParsingTest extends TestCase
             $this->parsePsrRequest('application/json', $body);
         }
 
-    public function testFailsParsingInvalidContentTypeRaw()
+    public function testFailsParsingInvalidContentTypeRaw() : void
     {
         $contentType = 'not-supported-content-type';
         $body = 'test';
@@ -243,7 +244,7 @@ class RequestParsingTest extends TestCase
         $this->parseRawRequest($contentType, $body);
     }
 
-    public function testFailsParsingInvalidContentTypePsr()
+    public function testFailsParsingInvalidContentTypePsr() : void
     {
         $contentType = 'not-supported-content-type';
         $body = 'test';
@@ -253,28 +254,28 @@ class RequestParsingTest extends TestCase
             $this->parseRawRequest($contentType, $body);
         }
 
-    public function testFailsWithMissingContentTypeRaw()
+    public function testFailsWithMissingContentTypeRaw() : void
     {
         $this->expectException(RequestError::class);
         $this->expectExceptionMessage('Missing "Content-Type" header');
             $this->parseRawRequest(null, 'test');
         }
 
-    public function testFailsWithMissingContentTypePsr()
+    public function testFailsWithMissingContentTypePsr() : void
     {
         $this->expectException(RequestError::class);
         $this->expectExceptionMessage('Missing "Content-Type" header');
             $this->parsePsrRequest(null, 'test');
     }
 
-    public function testFailsOnMethodsOtherThanPostOrGetRaw()
+    public function testFailsOnMethodsOtherThanPostOrGetRaw() : void
     {
         $this->expectException(RequestError::class);
         $this->expectExceptionMessage('HTTP Method "PUT" is not supported');
         $this->parseRawRequest('application/json', json_encode([]), "PUT");
     }
 
-    public function testFailsOnMethodsOtherThanPostOrGetPsr()
+    public function testFailsOnMethodsOtherThanPostOrGetPsr() : void
     {
         $this->expectException(RequestError::class);
         $this->expectExceptionMessage('HTTP Method "PUT" is not supported');
diff --git a/tests/Server/RequestValidationTest.php b/tests/Server/RequestValidationTest.php
index bff1e5e..e205bfd 100644
--- a/tests/Server/RequestValidationTest.php
+++ b/tests/Server/RequestValidationTest.php
@@ -7,7 +7,7 @@ use PHPUnit\Framework\TestCase;
 
 class RequestValidationTest extends TestCase
 {
-    public function testSimpleRequestShouldValidate()
+    public function testSimpleRequestShouldValidate() : void
     {
         $query = '{my q}';
         $variables = ['a' => 'b', 'c' => 'd'];
@@ -22,7 +22,7 @@ class RequestValidationTest extends TestCase
         $this->assertValid($parsedBody);
     }
 
-    public function testRequestWithQueryIdShouldValidate()
+    public function testRequestWithQueryIdShouldValidate() : void
     {
         $queryId = 'some-query-id';
         $variables = ['a' => 'b', 'c' => 'd'];
@@ -37,7 +37,7 @@ class RequestValidationTest extends TestCase
         $this->assertValid($parsedBody);
     }
 
-    public function testRequiresQueryOrQueryId()
+    public function testRequiresQueryOrQueryId() : void
     {
         $parsedBody = OperationParams::create([
             'variables' => ['foo' => 'bar'],
@@ -50,7 +50,7 @@ class RequestValidationTest extends TestCase
         );
     }
 
-    public function testFailsWhenBothQueryAndQueryIdArePresent()
+    public function testFailsWhenBothQueryAndQueryIdArePresent() : void
     {
         $parsedBody = OperationParams::create([
             'query' => '{my query}',
@@ -63,7 +63,7 @@ class RequestValidationTest extends TestCase
         );
     }
 
-    public function testFailsWhenQueryParameterIsNotString()
+    public function testFailsWhenQueryParameterIsNotString() : void
     {
         $parsedBody = OperationParams::create([
             'query' => ['t' => '{my query}']
@@ -75,7 +75,7 @@ class RequestValidationTest extends TestCase
         );
     }
 
-    public function testFailsWhenQueryIdParameterIsNotString()
+    public function testFailsWhenQueryIdParameterIsNotString() : void
     {
         $parsedBody = OperationParams::create([
             'queryId' => ['t' => '{my query}']
@@ -87,7 +87,7 @@ class RequestValidationTest extends TestCase
         );
     }
 
-    public function testFailsWhenOperationParameterIsNotString()
+    public function testFailsWhenOperationParameterIsNotString() : void
     {
         $parsedBody = OperationParams::create([
             'query' => '{my query}',
@@ -103,7 +103,7 @@ class RequestValidationTest extends TestCase
     /**
      * @see https://github.com/webonyx/graphql-php/issues/156
      */
-    public function testIgnoresNullAndEmptyStringVariables()
+    public function testIgnoresNullAndEmptyStringVariables() : void
     {
         $query = '{my q}';
         $parsedBody = OperationParams::create([
@@ -120,7 +120,7 @@ class RequestValidationTest extends TestCase
         $this->assertValid($parsedBody);
     }
 
-    public function testFailsWhenVariablesParameterIsNotObject()
+    public function testFailsWhenVariablesParameterIsNotObject() : void
     {
         $parsedBody = OperationParams::create([
             'query' => '{my query}',
diff --git a/tests/Server/ServerConfigTest.php b/tests/Server/ServerConfigTest.php
index 8e78f8f..d8af920 100644
--- a/tests/Server/ServerConfigTest.php
+++ b/tests/Server/ServerConfigTest.php
@@ -11,7 +11,7 @@ use PHPUnit\Framework\TestCase;
 
 class ServerConfigTest extends TestCase
 {
-    public function testDefaults()
+    public function testDefaults() : void
     {
         $config = ServerConfig::create();
         $this->assertEquals(null, $config->getSchema());
@@ -27,7 +27,7 @@ class ServerConfigTest extends TestCase
         $this->assertEquals(false, $config->getQueryBatching());
     }
 
-    public function testAllowsSettingSchema()
+    public function testAllowsSettingSchema() : void
     {
         $schema = new Schema(['query' => new ObjectType(['name' => 'a', 'fields' => []])]);
         $config = ServerConfig::create()
@@ -40,7 +40,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame($schema2, $config->getSchema());
     }
 
-    public function testAllowsSettingContext()
+    public function testAllowsSettingContext() : void
     {
         $config = ServerConfig::create();
 
@@ -53,7 +53,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame($context2, $config->getContext());
     }
 
-    public function testAllowsSettingRootValue()
+    public function testAllowsSettingRootValue() : void
     {
         $config = ServerConfig::create();
 
@@ -66,7 +66,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame($context2, $config->getRootValue());
     }
 
-    public function testAllowsSettingErrorFormatter()
+    public function testAllowsSettingErrorFormatter() : void
     {
         $config = ServerConfig::create();
 
@@ -79,7 +79,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame($formatter, $config->getErrorFormatter());
     }
 
-    public function testAllowsSettingErrorsHandler()
+    public function testAllowsSettingErrorsHandler() : void
     {
         $config = ServerConfig::create();
 
@@ -92,7 +92,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame($handler, $config->getErrorsHandler());
     }
 
-    public function testAllowsSettingPromiseAdapter()
+    public function testAllowsSettingPromiseAdapter() : void
     {
         $config = ServerConfig::create();
 
@@ -105,7 +105,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame($adapter2, $config->getPromiseAdapter());
     }
 
-    public function testAllowsSettingValidationRules()
+    public function testAllowsSettingValidationRules() : void
     {
         $config = ServerConfig::create();
 
@@ -122,7 +122,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame($rules, $config->getValidationRules());
     }
 
-    public function testAllowsSettingDefaultFieldResolver()
+    public function testAllowsSettingDefaultFieldResolver() : void
     {
         $config = ServerConfig::create();
 
@@ -135,7 +135,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame($resolver, $config->getFieldResolver());
     }
 
-    public function testAllowsSettingPersistedQueryLoader()
+    public function testAllowsSettingPersistedQueryLoader() : void
     {
         $config = ServerConfig::create();
 
@@ -148,7 +148,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame($loader, $config->getPersistentQueryLoader());
     }
 
-    public function testAllowsSettingCatchPhpErrors()
+    public function testAllowsSettingCatchPhpErrors() : void
     {
         $config = ServerConfig::create();
 
@@ -159,7 +159,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame(false, $config->getDebug());
     }
 
-    public function testAcceptsArray()
+    public function testAcceptsArray() : void
     {
         $arr = [
             'schema' => new \GraphQL\Type\Schema([
@@ -190,7 +190,7 @@ class ServerConfigTest extends TestCase
         $this->assertSame(true, $config->getQueryBatching());
     }
 
-    public function testThrowsOnInvalidArrayKey()
+    public function testThrowsOnInvalidArrayKey() : void
     {
         $arr = [
             'missingKey' => 'value'
@@ -202,7 +202,7 @@ class ServerConfigTest extends TestCase
         ServerConfig::create($arr);
     }
 
-    public function testInvalidValidationRules()
+    public function testInvalidValidationRules() : void
     {
         $rules = new \stdClass();
         $config = ServerConfig::create();
diff --git a/tests/Server/StandardServerTest.php b/tests/Server/StandardServerTest.php
index 3f9398b..5c22788 100644
--- a/tests/Server/StandardServerTest.php
+++ b/tests/Server/StandardServerTest.php
@@ -22,7 +22,7 @@ class StandardServerTest extends ServerTestCase
             ->setSchema($schema);
     }
 
-    public function testSimpleRequestExecutionWithOutsideParsing()
+    public function testSimpleRequestExecutionWithOutsideParsing() : void
     {
         $body = json_encode([
             'query' => '{f1}'
@@ -41,7 +41,7 @@ class StandardServerTest extends ServerTestCase
         $this->assertEquals($expected, $result->toArray(true));
     }
 
-    public function testSimplePsrRequestExecution()
+    public function testSimplePsrRequestExecution() : void
     {
         $body = [
             'query' => '{f1}'
@@ -57,7 +57,7 @@ class StandardServerTest extends ServerTestCase
         $this->assertPsrRequestEquals($expected, $request);
     }
 
-    public function testMultipleOperationPsrRequestExecution()
+    public function testMultipleOperationPsrRequestExecution() : void
     {
         $body = [
             'query' => 'query firstOp {fieldWithPhpError} query secondOp {f1}',
diff --git a/tests/StarWarsIntrospectionTest.php b/tests/StarWarsIntrospectionTest.php
index 3d961fa..07c605e 100644
--- a/tests/StarWarsIntrospectionTest.php
+++ b/tests/StarWarsIntrospectionTest.php
@@ -12,7 +12,7 @@ class StarWarsIntrospectionTest extends TestCase
     /**
      * @see it('Allows querying the schema for types')
      */
-    public function testAllowsQueryingTheSchemaForTypes()
+    public function testAllowsQueryingTheSchemaForTypes() : void
     {
         $query = '
         query IntrospectionTypeQuery {
@@ -53,7 +53,7 @@ class StarWarsIntrospectionTest extends TestCase
     /**
      * @see it('Allows querying the schema for query type')
      */
-    public function testAllowsQueryingTheSchemaForQueryType()
+    public function testAllowsQueryingTheSchemaForQueryType() : void
     {
         $query = '
         query IntrospectionQueryTypeQuery {
@@ -77,7 +77,7 @@ class StarWarsIntrospectionTest extends TestCase
     /**
      * @see it('Allows querying the schema for a specific type')
      */
-    public function testAllowsQueryingTheSchemaForASpecificType()
+    public function testAllowsQueryingTheSchemaForASpecificType() : void
     {
         $query = '
         query IntrospectionDroidTypeQuery {
@@ -97,7 +97,7 @@ class StarWarsIntrospectionTest extends TestCase
     /**
      * @see it('Allows querying the schema for an object kind')
      */
-    public function testAllowsQueryingForAnObjectKind()
+    public function testAllowsQueryingForAnObjectKind() : void
     {
         $query = '
         query IntrospectionDroidKindQuery {
@@ -119,7 +119,7 @@ class StarWarsIntrospectionTest extends TestCase
     /**
      * @see it('Allows querying the schema for an interface kind')
      */
-    public function testAllowsQueryingForInterfaceKind()
+    public function testAllowsQueryingForInterfaceKind() : void
     {
         $query = '
         query IntrospectionCharacterKindQuery {
@@ -141,7 +141,7 @@ class StarWarsIntrospectionTest extends TestCase
     /**
      * @see it('Allows querying the schema for object fields')
      */
-    public function testAllowsQueryingForObjectFields()
+    public function testAllowsQueryingForObjectFields() : void
     {
         $query = '
         query IntrospectionDroidFieldsQuery {
@@ -212,7 +212,7 @@ class StarWarsIntrospectionTest extends TestCase
     /**
      * @see it('Allows querying the schema for nested object fields')
      */
-    public function testAllowsQueryingTheSchemaForNestedObjectFields()
+    public function testAllowsQueryingTheSchemaForNestedObjectFields() : void
     {
         $query = '
         query IntrospectionDroidNestedFieldsQuery {
@@ -302,7 +302,7 @@ class StarWarsIntrospectionTest extends TestCase
     /**
      * @see it('Allows querying the schema for field args')
      */
-    public function testAllowsQueryingTheSchemaForFieldArgs()
+    public function testAllowsQueryingTheSchemaForFieldArgs() : void
     {
         $query = '
         query IntrospectionQueryTypeQuery {
@@ -396,7 +396,7 @@ class StarWarsIntrospectionTest extends TestCase
     /**
      * @see it('Allows querying the schema for documentation')
      */
-    public function testAllowsQueryingTheSchemaForDocumentation()
+    public function testAllowsQueryingTheSchemaForDocumentation() : void
     {
         $query = '
         query IntrospectionDroidDescriptionQuery {
diff --git a/tests/StarWarsQueryTest.php b/tests/StarWarsQueryTest.php
index c4396b2..aa478dd 100644
--- a/tests/StarWarsQueryTest.php
+++ b/tests/StarWarsQueryTest.php
@@ -13,7 +13,7 @@ class StarWarsQueryTest extends TestCase
     /**
      * @see it('Correctly identifies R2-D2 as the hero of the Star Wars Saga')
      */
-    public function testCorrectlyIdentifiesR2D2AsTheHeroOfTheStarWarsSaga()
+    public function testCorrectlyIdentifiesR2D2AsTheHeroOfTheStarWarsSaga() : void
     {
         $query = '
         query HeroNameQuery {
@@ -33,7 +33,7 @@ class StarWarsQueryTest extends TestCase
     /**
      * @see it('Allows us to query for the ID and friends of R2-D2')
      */
-    public function testAllowsUsToQueryForTheIDAndFriendsOfR2D2()
+    public function testAllowsUsToQueryForTheIDAndFriendsOfR2D2() : void
     {
         $query = '
         query HeroNameAndFriendsQuery {
@@ -71,7 +71,7 @@ class StarWarsQueryTest extends TestCase
     /**
      * @see it('Allows us to query for the friends of friends of R2-D2')
      */
-    public function testAllowsUsToQueryForTheFriendsOfFriendsOfR2D2()
+    public function testAllowsUsToQueryForTheFriendsOfFriendsOfR2D2() : void
     {
         $query = '
         query NestedQuery {
@@ -132,7 +132,7 @@ class StarWarsQueryTest extends TestCase
     /**
      * @see it('Using IDs and query parameters to refetch objects')
      */
-    public function testAllowsUsToQueryForLukeSkywalkerDirectlyUsingHisID()
+    public function testAllowsUsToQueryForLukeSkywalkerDirectlyUsingHisID() : void
     {
         $query = '
         query FetchLukeQuery {
@@ -153,7 +153,7 @@ class StarWarsQueryTest extends TestCase
     /**
      * @see it('Allows us to create a generic query, then use it to fetch Luke Skywalker using his ID')
      */
-    public function testGenericQueryToGetLukeSkywalkerById()
+    public function testGenericQueryToGetLukeSkywalkerById() : void
     {
         $query = '
         query FetchSomeIDQuery($someId: String!) {
@@ -177,7 +177,7 @@ class StarWarsQueryTest extends TestCase
     /**
      * @see it('Allows us to create a generic query, then use it to fetch Han Solo using his ID')
      */
-    public function testGenericQueryToGetHanSoloById()
+    public function testGenericQueryToGetHanSoloById() : void
     {
         $query = '
         query FetchSomeIDQuery($someId: String!) {
@@ -200,7 +200,7 @@ class StarWarsQueryTest extends TestCase
     /**
      * @see it('Allows us to create a generic query, then pass an invalid ID to get null back')
      */
-    public function testGenericQueryWithInvalidId()
+    public function testGenericQueryWithInvalidId() : void
     {
         $query = '
         query humanQuery($id: String!) {
@@ -335,7 +335,7 @@ class StarWarsQueryTest extends TestCase
     /**
      * @see it('Using __typename to find the type of an object')
      */
-    public function testVerifyThatR2D2IsADroid()
+    public function testVerifyThatR2D2IsADroid() : void
     {
         $query = '
         query CheckTypeOfR2 {
@@ -357,7 +357,7 @@ class StarWarsQueryTest extends TestCase
     /**
      * @see it('Allows us to verify that Luke is a human')
      */
-    public function testVerifyThatLukeIsHuman()
+    public function testVerifyThatLukeIsHuman() : void
     {
         $query = '
         query CheckTypeOfLuke {
diff --git a/tests/StarWarsValidationTest.php b/tests/StarWarsValidationTest.php
index d66caa9..a4b0018 100644
--- a/tests/StarWarsValidationTest.php
+++ b/tests/StarWarsValidationTest.php
@@ -13,7 +13,7 @@ class StarWarsValidationTest extends TestCase
     /**
      * @see it('Validates a complex but valid query')
      */
-    public function testValidatesAComplexButValidQuery()
+    public function testValidatesAComplexButValidQuery() : void
     {
         $query = '
         query NestedQueryWithFragment {
@@ -40,7 +40,7 @@ class StarWarsValidationTest extends TestCase
     /**
      * @see it('Notes that non-existent fields are invalid')
      */
-    public function testThatNonExistentFieldsAreInvalid()
+    public function testThatNonExistentFieldsAreInvalid() : void
     {
         $query = '
         query HeroSpaceshipQuery {
@@ -56,7 +56,7 @@ class StarWarsValidationTest extends TestCase
     /**
      * @see it('Requires fields on objects')
      */
-    public function testRequiresFieldsOnObjects()
+    public function testRequiresFieldsOnObjects() : void
     {
         $query = '
         query HeroNoFieldsQuery {
@@ -71,7 +71,7 @@ class StarWarsValidationTest extends TestCase
     /**
      * @see it('Disallows fields on scalars')
      */
-    public function testDisallowsFieldsOnScalars()
+    public function testDisallowsFieldsOnScalars() : void
     {
       $query = '
         query HeroFieldsOnScalarQuery {
@@ -89,7 +89,7 @@ class StarWarsValidationTest extends TestCase
     /**
      * @see it('Disallows object fields on interfaces')
      */
-    public function testDisallowsObjectFieldsOnInterfaces()
+    public function testDisallowsObjectFieldsOnInterfaces() : void
     {
         $query = '
         query DroidFieldOnCharacter {
@@ -106,7 +106,7 @@ class StarWarsValidationTest extends TestCase
     /**
      * @see it('Allows object fields in fragments')
      */
-    public function testAllowsObjectFieldsInFragments()
+    public function testAllowsObjectFieldsInFragments() : void
     {
         $query = '
         query DroidFieldInFragment {
@@ -127,7 +127,7 @@ class StarWarsValidationTest extends TestCase
     /**
      * @see it('Allows object fields in inline fragments')
      */
-    public function testAllowsObjectFieldsInInlineFragments()
+    public function testAllowsObjectFieldsInInlineFragments() : void
     {
         $query = '
         query DroidFieldInFragment {
diff --git a/tests/Type/DefinitionTest.php b/tests/Type/DefinitionTest.php
index 8bd5cf1..d5b6b50 100644
--- a/tests/Type/DefinitionTest.php
+++ b/tests/Type/DefinitionTest.php
@@ -172,7 +172,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('defines a query only schema')
      */
-    public function testDefinesAQueryOnlySchema()
+    public function testDefinesAQueryOnlySchema() : void
     {
         $blogSchema = new Schema([
             'query' => $this->blogQuery
@@ -216,7 +216,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('defines a mutation schema')
      */
-    public function testDefinesAMutationSchema()
+    public function testDefinesAMutationSchema() : void
     {
         $schema = new Schema([
             'query' => $this->blogQuery,
@@ -235,7 +235,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('defines a subscription schema')
      */
-    public function testDefinesSubscriptionSchema()
+    public function testDefinesSubscriptionSchema() : void
     {
         $schema = new Schema([
             'query' => $this->blogQuery,
@@ -253,7 +253,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('defines an enum type with deprecated value')
      */
-    public function testDefinesEnumTypeWithDeprecatedValue()
+    public function testDefinesEnumTypeWithDeprecatedValue() : void
     {
         $enumTypeWithDeprecatedValue = new EnumType([
             'name' => 'EnumWithDeprecatedValue',
@@ -278,7 +278,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('defines an enum type with a value of `null` and `undefined`')
      */
-    public function testDefinesAnEnumTypeWithAValueOfNullAndUndefined()
+    public function testDefinesAnEnumTypeWithAValueOfNullAndUndefined() : void
     {
         $EnumTypeWithNullishValue = new EnumType([
             'name' => 'EnumWithNullishValue',
@@ -315,7 +315,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('defines an object type with deprecated field')
      */
-    public function testDefinesAnObjectTypeWithDeprecatedField()
+    public function testDefinesAnObjectTypeWithDeprecatedField() : void
     {
         $TypeWithDeprecatedField = new ObjectType([
           'name' => 'foo',
@@ -339,7 +339,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('includes nested input objects in the map')
      */
-    public function testIncludesNestedInputObjectInTheMap()
+    public function testIncludesNestedInputObjectInTheMap() : void
     {
         $nestedInputObject = new InputObjectType([
             'name' => 'NestedInputObject',
@@ -369,7 +369,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('includes interface possible types in the type map')
      */
-    public function testIncludesInterfaceSubtypesInTheTypeMap()
+    public function testIncludesInterfaceSubtypesInTheTypeMap() : void
     {
         $someInterface = new InterfaceType([
             'name' => 'SomeInterface',
@@ -401,7 +401,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('includes interfaces' thunk subtypes in the type map')
      */
-    public function testIncludesInterfacesThunkSubtypesInTheTypeMap()
+    public function testIncludesInterfacesThunkSubtypesInTheTypeMap() : void
     {
         $someInterface = null;
 
@@ -436,7 +436,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('stringifies simple types')
      */
-    public function testStringifiesSimpleTypes()
+    public function testStringifiesSimpleTypes() : void
     {
         $this->assertSame('Int', (string) Type::int());
         $this->assertSame('Article', (string) $this->blogArticle);
@@ -457,7 +457,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('JSON stringifies simple types')
      */
-    public function testJSONStringifiesSimpleTypes()
+    public function testJSONStringifiesSimpleTypes() : void
     {
         $this->assertEquals('"Int"', json_encode(Type::int()));
         $this->assertEquals('"Article"', json_encode($this->blogArticle));
@@ -475,7 +475,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('identifies input types')
      */
-    public function testIdentifiesInputTypes()
+    public function testIdentifiesInputTypes() : void
     {
         $expected = [
             [Type::int(), true],
@@ -494,7 +494,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('identifies output types')
      */
-    public function testIdentifiesOutputTypes()
+    public function testIdentifiesOutputTypes() : void
     {
         $expected = [
             [Type::int(), true],
@@ -513,7 +513,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('prohibits nesting NonNull inside NonNull')
      */
-    public function testProhibitsNestingNonNullInsideNonNull()
+    public function testProhibitsNestingNonNullInsideNonNull() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -525,7 +525,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('allows a thunk for Union member types')
      */
-    public function testAllowsThunkForUnionTypes()
+    public function testAllowsThunkForUnionTypes() : void
     {
         $union = new UnionType([
             'name' => 'ThunkUnion',
@@ -537,7 +537,7 @@ class DefinitionTest extends TestCase
         $this->assertSame($this->objectType, $types[0]);
     }
 
-    public function testAllowsRecursiveDefinitions()
+    public function testAllowsRecursiveDefinitions() : void
     {
         // See https://github.com/webonyx/graphql-php/issues/16
         $node = new InterfaceType([
@@ -602,7 +602,7 @@ class DefinitionTest extends TestCase
         $this->assertSame($user, $blog->getField('owner')->getType()->getWrappedType(true));
     }
 
-    public function testInputObjectTypeAllowsRecursiveDefinitions()
+    public function testInputObjectTypeAllowsRecursiveDefinitions() : void
     {
         $called = false;
         $inputObject = new InputObjectType([
@@ -637,7 +637,7 @@ class DefinitionTest extends TestCase
         $this->assertSame($someMutation->getField('mutateSomething')->getArg('input')->getType(), $inputObject);
     }
 
-    public function testInterfaceTypeAllowsRecursiveDefinitions()
+    public function testInterfaceTypeAllowsRecursiveDefinitions() : void
     {
         $called = false;
         $interface = new InterfaceType([
@@ -669,7 +669,7 @@ class DefinitionTest extends TestCase
         $this->assertSame($interface->getField('value')->getType(), Type::string());
     }
 
-    public function testAllowsShorthandFieldDefinition()
+    public function testAllowsShorthandFieldDefinition() : void
     {
         $interface = new InterfaceType([
             'name' => 'SomeInterface',
@@ -715,7 +715,7 @@ class DefinitionTest extends TestCase
         $this->assertEquals('test', $testField->name);
     }
 
-    public function testInfersNameFromClassname()
+    public function testInfersNameFromClassname() : void
     {
         $myObj = new MyCustomType();
         $this->assertEquals('MyCustom', $myObj->name);
@@ -724,7 +724,7 @@ class DefinitionTest extends TestCase
         $this->assertEquals('OtherCustom', $otherCustom->name);
     }
 
-    public function testAllowsOverridingInternalTypes()
+    public function testAllowsOverridingInternalTypes() : void
     {
         $idType = new CustomScalarType([
             'name' => 'ID',
@@ -746,7 +746,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Object type with a field function')
      */
-    public function testAcceptsAnObjectTypeWithAFieldFunction()
+    public function testAcceptsAnObjectTypeWithAFieldFunction() : void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
@@ -763,7 +763,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Object type field with undefined config')
      */
-    public function testRejectsAnObjectTypeFieldWithUndefinedConfig()
+    public function testRejectsAnObjectTypeFieldWithUndefinedConfig() : void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
@@ -781,7 +781,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Object type with incorrectly typed fields')
      */
-    public function testRejectsAnObjectTypeWithIncorrectlyTypedFields()
+    public function testRejectsAnObjectTypeWithIncorrectlyTypedFields() : void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
@@ -798,7 +798,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Object type with a field function that returns incorrect type')
      */
-    public function testRejectsAnObjectTypeWithAFieldFunctionThatReturnsIncorrectType()
+    public function testRejectsAnObjectTypeWithAFieldFunctionThatReturnsIncorrectType() : void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
@@ -819,7 +819,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Object type with field args')
      */
-    public function testAcceptsAnObjectTypeWithFieldArgs()
+    public function testAcceptsAnObjectTypeWithFieldArgs() : void
     {
         $this->expectNotToPerformAssertions();
         $objType = new ObjectType([
@@ -842,7 +842,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('does not allow isDeprecated without deprecationReason on field')
      */
-    public function testDoesNotAllowIsDeprecatedWithoutDeprecationReasonOnField()
+    public function testDoesNotAllowIsDeprecatedWithoutDeprecationReasonOnField() : void
     {
         $OldObject = new ObjectType([
             'name' => 'OldObject',
@@ -866,7 +866,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Object type with array interfaces')
      */
-    public function testAcceptsAnObjectTypeWithArrayInterfaces()
+    public function testAcceptsAnObjectTypeWithArrayInterfaces() : void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
@@ -879,7 +879,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Object type with interfaces as a function returning an array')
      */
-    public function testAcceptsAnObjectTypeWithInterfacesAsAFunctionReturningAnArray()
+    public function testAcceptsAnObjectTypeWithInterfacesAsAFunctionReturningAnArray() : void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
@@ -894,7 +894,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Object type with incorrectly typed interfaces')
      */
-    public function testRejectsAnObjectTypeWithIncorrectlyTypedInterfaces()
+    public function testRejectsAnObjectTypeWithIncorrectlyTypedInterfaces() : void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
@@ -911,7 +911,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Object type with interfaces as a function returning an incorrect type')
      */
-    public function testRejectsAnObjectTypeWithInterfacesAsAFunctionReturningAnIncorrectType()
+    public function testRejectsAnObjectTypeWithInterfacesAsAFunctionReturningAnIncorrectType() : void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
@@ -956,7 +956,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a lambda as an Object field resolver')
      */
-    public function testAcceptsALambdaAsAnObjectFieldResolver()
+    public function testAcceptsALambdaAsAnObjectFieldResolver() : void
     {
         $this->expectNotToPerformAssertions();
         // should not throw:
@@ -966,7 +966,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an empty Object field resolver')
      */
-    public function testRejectsAnEmptyObjectFieldResolver()
+    public function testRejectsAnEmptyObjectFieldResolver() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -978,7 +978,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a constant scalar value resolver')
      */
-    public function testRejectsAConstantScalarValueResolver()
+    public function testRejectsAConstantScalarValueResolver() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1005,7 +1005,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Interface type defining resolveType')
      */
-    public function testAcceptsAnInterfaceTypeDefiningResolveType()
+    public function testAcceptsAnInterfaceTypeDefiningResolveType() : void
     {
         $this->expectNotToPerformAssertions();
         $AnotherInterfaceType = new InterfaceType([
@@ -1026,7 +1026,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Interface with implementing type defining isTypeOf')
      */
-    public function testAcceptsAnInterfaceWithImplementingTypeDefiningIsTypeOf()
+    public function testAcceptsAnInterfaceWithImplementingTypeDefiningIsTypeOf() : void
     {
         $this->expectNotToPerformAssertions();
         $InterfaceTypeWithoutResolveType = new InterfaceType([
@@ -1047,7 +1047,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Interface type defining resolveType with implementing type defining isTypeOf')
      */
-    public function testAcceptsAnInterfaceTypeDefiningResolveTypeWithImplementingTypeDefiningIsTypeOf()
+    public function testAcceptsAnInterfaceTypeDefiningResolveTypeWithImplementingTypeDefiningIsTypeOf() : void
     {
         $this->expectNotToPerformAssertions();
         $AnotherInterfaceType = new InterfaceType([
@@ -1068,7 +1068,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Interface type with an incorrect type for resolveType')
      */
-    public function testRejectsAnInterfaceTypeWithAnIncorrectTypeForResolveType()
+    public function testRejectsAnInterfaceTypeWithAnIncorrectTypeForResolveType() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1096,7 +1096,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a Union type defining resolveType')
      */
-    public function testAcceptsAUnionTypeDefiningResolveType()
+    public function testAcceptsAUnionTypeDefiningResolveType() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw:
@@ -1111,7 +1111,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a Union of Object types defining isTypeOf')
      */
-    public function testAcceptsAUnionOfObjectTypesDefiningIsTypeOf()
+    public function testAcceptsAUnionOfObjectTypesDefiningIsTypeOf() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw:
@@ -1126,7 +1126,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a Union type defining resolveType of Object types defining isTypeOf')
      */
-    public function testAcceptsAUnionTypeDefiningResolveTypeOfObjectTypesDefiningIsTypeOf()
+    public function testAcceptsAUnionTypeDefiningResolveTypeOfObjectTypesDefiningIsTypeOf() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw:
@@ -1141,7 +1141,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Union type with an incorrect type for resolveType')
      */
-    public function testRejectsAnUnionTypeWithAnIncorrectTypeForResolveType()
+    public function testRejectsAnUnionTypeWithAnIncorrectTypeForResolveType() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1161,7 +1161,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a Scalar type defining serialize')
      */
-    public function testAcceptsAScalarTypeDefiningSerialize()
+    public function testAcceptsAScalarTypeDefiningSerialize() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw
@@ -1178,7 +1178,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Scalar type not defining serialize')
      */
-    public function testRejectsAScalarTypeNotDefiningSerialize()
+    public function testRejectsAScalarTypeNotDefiningSerialize() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1196,7 +1196,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Scalar type defining serialize with an incorrect type')
      */
-    public function testRejectsAScalarTypeDefiningSerializeWithAnIncorrectType()
+    public function testRejectsAScalarTypeDefiningSerializeWithAnIncorrectType() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1215,7 +1215,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a Scalar type defining parseValue and parseLiteral')
      */
-    public function testAcceptsAScalarTypeDefiningParseValueAndParseLiteral()
+    public function testAcceptsAScalarTypeDefiningParseValueAndParseLiteral() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw:
@@ -1235,7 +1235,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Scalar type defining parseValue but not parseLiteral')
      */
-    public function testRejectsAScalarTypeDefiningParseValueButNotParseLiteral()
+    public function testRejectsAScalarTypeDefiningParseValueButNotParseLiteral() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1255,7 +1255,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Scalar type defining parseLiteral but not parseValue')
      */
-    public function testRejectsAScalarTypeDefiningParseLiteralButNotParseValue()
+    public function testRejectsAScalarTypeDefiningParseLiteralButNotParseValue() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1275,7 +1275,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Scalar type defining parseValue and parseLiteral with an incorrect type')
      */
-    public function testRejectsAScalarTypeDefiningParseValueAndParseLiteralWithAnIncorrectType()
+    public function testRejectsAScalarTypeDefiningParseValueAndParseLiteralWithAnIncorrectType() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1297,7 +1297,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Object type with an isTypeOf function')
      */
-    public function testAcceptsAnObjectTypeWithAnIsTypeOfFunction()
+    public function testAcceptsAnObjectTypeWithAnIsTypeOfFunction() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw
@@ -1312,7 +1312,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Object type with an incorrect type for isTypeOf')
      */
-    public function testRejectsAnObjectTypeWithAnIncorrectTypeForIsTypeOf()
+    public function testRejectsAnObjectTypeWithAnIncorrectTypeForIsTypeOf() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1332,7 +1332,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a Union type with array types')
      */
-    public function testAcceptsAUnionTypeWithArrayTypes()
+    public function testAcceptsAUnionTypeWithArrayTypes() : void
     {
         $this->expectNotToPerformAssertions();
         // Should not throw:
@@ -1347,7 +1347,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a Union type with function returning an array of types')
      */
-    public function testAcceptsAUnionTypeWithFunctionReturningAnArrayOfTypes()
+    public function testAcceptsAUnionTypeWithFunctionReturningAnArrayOfTypes() : void
     {
         $this->expectNotToPerformAssertions();
         $this->schemaWithFieldType(
@@ -1363,7 +1363,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Union type without types')
      */
-    public function testRejectsAUnionTypeWithoutTypes()
+    public function testRejectsAUnionTypeWithoutTypes() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1379,7 +1379,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Union type with incorrectly typed types')
      */
-    public function testRejectsAUnionTypeWithIncorrectlyTypedTypes()
+    public function testRejectsAUnionTypeWithIncorrectlyTypedTypes() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage(
@@ -1398,7 +1398,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Input Object type with fields')
      */
-    public function testAcceptsAnInputObjectTypeWithFields()
+    public function testAcceptsAnInputObjectTypeWithFields() : void
     {
         $inputObjType = new InputObjectType([
             'name' => 'SomeInputObject',
@@ -1413,7 +1413,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts an Input Object type with a field function')
      */
-    public function testAcceptsAnInputObjectTypeWithAFieldFunction()
+    public function testAcceptsAnInputObjectTypeWithAFieldFunction() : void
     {
         $inputObjType = new InputObjectType([
             'name' => 'SomeInputObject',
@@ -1430,7 +1430,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Input Object type with incorrect fields')
      */
-    public function testRejectsAnInputObjectTypeWithIncorrectFields()
+    public function testRejectsAnInputObjectTypeWithIncorrectFields() : void
     {
         $inputObjType = new InputObjectType([
             'name' => 'SomeInputObject',
@@ -1447,7 +1447,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Input Object type with fields function that returns incorrect type')
      */
-    public function testRejectsAnInputObjectTypeWithFieldsFunctionThatReturnsIncorrectType()
+    public function testRejectsAnInputObjectTypeWithFieldsFunctionThatReturnsIncorrectType() : void
     {
         $inputObjType = new InputObjectType([
             'name' => 'SomeInputObject',
@@ -1468,7 +1468,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Input Object type with resolvers')
      */
-    public function testRejectsAnInputObjectTypeWithResolvers()
+    public function testRejectsAnInputObjectTypeWithResolvers() : void
     {
         $inputObjType = new InputObjectType([
             'name' => 'SomeInputObject',
@@ -1492,7 +1492,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Input Object type with resolver constant')
      */
-    public function testRejectsAnInputObjectTypeWithResolverConstant()
+    public function testRejectsAnInputObjectTypeWithResolverConstant() : void
     {
         $inputObjType = new InputObjectType([
             'name' => 'SomeInputObject',
@@ -1516,7 +1516,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a well defined Enum type with empty value definition')
      */
-    public function testAcceptsAWellDefinedEnumTypeWithEmptyValueDefinition()
+    public function testAcceptsAWellDefinedEnumTypeWithEmptyValueDefinition() : void
     {
         $enumType = new EnumType([
             'name' => 'SomeEnum',
@@ -1532,7 +1532,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('accepts a well defined Enum type with internal value definition')
      */
-    public function testAcceptsAWellDefinedEnumTypeWithInternalValueDefinition()
+    public function testAcceptsAWellDefinedEnumTypeWithInternalValueDefinition() : void
     {
         $enumType = new EnumType([
             'name' => 'SomeEnum',
@@ -1548,7 +1548,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects an Enum type with incorrectly typed values')
      */
-    public function testRejectsAnEnumTypeWithIncorrectlyTypedValues()
+    public function testRejectsAnEnumTypeWithIncorrectlyTypedValues() : void
     {
         $enumType = new EnumType([
             'name' => 'SomeEnum',
@@ -1564,7 +1564,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('does not allow isDeprecated without deprecationReason on enum')
      */
-    public function testDoesNotAllowIsDeprecatedWithoutDeprecationReasonOnEnum()
+    public function testDoesNotAllowIsDeprecatedWithoutDeprecationReasonOnEnum() : void
     {
         $enumType = new EnumType([
             'name' => 'SomeEnum',
@@ -1582,9 +1582,11 @@ class DefinitionTest extends TestCase
         $enumType->assertValid();
     }
 
-    // Type System: List must accept only types
 
-    public function testListMustAcceptOnlyTypes()
+    /**
+     * Type System: List must accept only types
+     */
+    public function testListMustAcceptOnlyTypes() : void
     {
         $types = [
             Type::string(),
@@ -1618,9 +1620,11 @@ class DefinitionTest extends TestCase
         }
     }
 
-    // Type System: NonNull must only accept non-nullable types
 
-    public function testNonNullMustOnlyAcceptNonNullableTypes()
+    /**
+     * Type System: NonNull must only accept non-nullable types
+     */
+    public function testNonNullMustOnlyAcceptNonNullableTypes() : void
     {
         $nullableTypes = [
             Type::string(),
@@ -1663,7 +1667,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Schema which redefines a built-in type')
      */
-    public function testRejectsASchemaWhichRedefinesABuiltInType()
+    public function testRejectsASchemaWhichRedefinesABuiltInType() : void
     {
         $FakeString = new CustomScalarType([
             'name' => 'String',
@@ -1691,7 +1695,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Schema which defines an object type twice')
      */
-    public function testRejectsASchemaWhichDefinesAnObjectTypeTwice()
+    public function testRejectsASchemaWhichDefinesAnObjectTypeTwice() : void
     {
         $A = new ObjectType([
             'name' => 'SameName',
@@ -1722,7 +1726,7 @@ class DefinitionTest extends TestCase
     /**
      * @see it('rejects a Schema which have same named objects implementing an interface')
      */
-    public function testRejectsASchemaWhichHaveSameNamedObjectsImplementingAnInterface()
+    public function testRejectsASchemaWhichHaveSameNamedObjectsImplementingAnInterface() : void
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
diff --git a/tests/Type/EnumTypeTest.php b/tests/Type/EnumTypeTest.php
index 4a5b376..f8ab00a 100644
--- a/tests/Type/EnumTypeTest.php
+++ b/tests/Type/EnumTypeTest.php
@@ -182,7 +182,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('accepts enum literals as input')
      */
-    public function testAcceptsEnumLiteralsAsInput()
+    public function testAcceptsEnumLiteralsAsInput() : void
     {
         $this->assertEquals(
             ['data' => ['colorInt' => 1]],
@@ -193,7 +193,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('enum may be output type')
      */
-    public function testEnumMayBeOutputType()
+    public function testEnumMayBeOutputType() : void
     {
         $this->assertEquals(
             ['data' => ['colorEnum' => 'GREEN']],
@@ -204,7 +204,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('enum may be both input and output type')
      */
-    public function testEnumMayBeBothInputAndOutputType()
+    public function testEnumMayBeBothInputAndOutputType() : void
     {
         $this->assertEquals(
             ['data' => ['colorEnum' => 'GREEN']],
@@ -215,7 +215,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('does not accept string literals')
      */
-    public function testDoesNotAcceptStringLiterals()
+    public function testDoesNotAcceptStringLiterals() : void
     {
         $this->expectFailure(
             '{ colorEnum(fromEnum: "GREEN") }',
@@ -230,7 +230,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('does not accept valuesNotInTheEnum')
      */
-    public function testDoesNotAcceptValuesNotInTheEnum()
+    public function testDoesNotAcceptValuesNotInTheEnum() : void
     {
         $this->expectFailure(
             '{ colorEnum(fromEnum: GREENISH) }',
@@ -245,7 +245,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('does not accept values with incorrect casing')
      */
-    public function testDoesNotAcceptValuesWithIncorrectCasing()
+    public function testDoesNotAcceptValuesWithIncorrectCasing() : void
     {
         $this->expectFailure(
             '{ colorEnum(fromEnum: green) }',
@@ -260,7 +260,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('does not accept incorrect internal value')
      */
-    public function testDoesNotAcceptIncorrectInternalValue()
+    public function testDoesNotAcceptIncorrectInternalValue() : void
     {
         $this->expectFailure(
             '{ colorEnum(fromString: "GREEN") }',
@@ -276,7 +276,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('does not accept internal value in place of enum literal')
      */
-    public function testDoesNotAcceptInternalValueInPlaceOfEnumLiteral()
+    public function testDoesNotAcceptInternalValueInPlaceOfEnumLiteral() : void
     {
         $this->expectFailure(
             '{ colorEnum(fromEnum: 1) }',
@@ -288,7 +288,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('does not accept enum literal in place of int')
      */
-    public function testDoesNotAcceptEnumLiteralInPlaceOfInt()
+    public function testDoesNotAcceptEnumLiteralInPlaceOfInt() : void
     {
         $this->expectFailure(
             '{ colorEnum(fromInt: GREEN) }',
@@ -300,7 +300,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('accepts JSON string as enum variable')
      */
-    public function testAcceptsJSONStringAsEnumVariable()
+    public function testAcceptsJSONStringAsEnumVariable() : void
     {
         $this->assertEquals(
             ['data' => ['colorEnum' => 'BLUE']],
@@ -317,7 +317,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('accepts enum literals as input arguments to mutations')
      */
-    public function testAcceptsEnumLiteralsAsInputArgumentsToMutations()
+    public function testAcceptsEnumLiteralsAsInputArgumentsToMutations() : void
     {
         $this->assertEquals(
             ['data' => ['favoriteEnum' => 'GREEN']],
@@ -335,7 +335,7 @@ class EnumTypeTest extends TestCase
      * @see it('accepts enum literals as input arguments to subscriptions')
      * @todo
      */
-    public function testAcceptsEnumLiteralsAsInputArgumentsToSubscriptions()
+    public function testAcceptsEnumLiteralsAsInputArgumentsToSubscriptions() : void
     {
         $this->assertEquals(
             ['data' => ['subscribeToEnum' => 'GREEN']],
@@ -352,7 +352,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('does not accept internal value as enum variable')
      */
-    public function testDoesNotAcceptInternalValueAsEnumVariable()
+    public function testDoesNotAcceptInternalValueAsEnumVariable() : void
     {
         $this->expectFailure(
             'query test($color: Color!) { colorEnum(fromEnum: $color) }',
@@ -364,7 +364,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('does not accept string variables as enum input')
      */
-    public function testDoesNotAcceptStringVariablesAsEnumInput()
+    public function testDoesNotAcceptStringVariablesAsEnumInput() : void
     {
         $this->expectFailure(
             'query test($color: String!) { colorEnum(fromEnum: $color) }',
@@ -376,7 +376,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('does not accept internal value variable as enum input')
      */
-    public function testDoesNotAcceptInternalValueVariableSsEnumInput()
+    public function testDoesNotAcceptInternalValueVariableSsEnumInput() : void
     {
         $this->expectFailure(
             'query test($color: Int!) { colorEnum(fromEnum: $color) }',
@@ -388,7 +388,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('enum value may have an internal value of 0')
      */
-    public function testEnumValueMayHaveAnInternalValueOf0()
+    public function testEnumValueMayHaveAnInternalValueOf0() : void
     {
         $this->assertEquals(
             ['data' => ['colorEnum' => 'RED', 'colorInt' => 0]],
@@ -402,7 +402,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('enum inputs may be nullable')
      */
-    public function testEnumInputsMayBeNullable()
+    public function testEnumInputsMayBeNullable() : void
     {
         $this->assertEquals(
             ['data' => ['colorEnum' => null, 'colorInt' => null]],
@@ -416,7 +416,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('presents a getValues() API for complex enums')
      */
-    public function testPresentsGetValuesAPIForComplexEnums()
+    public function testPresentsGetValuesAPIForComplexEnums() : void
     {
         $ComplexEnum = $this->ComplexEnum;
         $values = $ComplexEnum->getValues();
@@ -431,7 +431,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('presents a getValue() API for complex enums')
      */
-    public function testPresentsGetValueAPIForComplexEnums()
+    public function testPresentsGetValueAPIForComplexEnums() : void
     {
         $oneValue = $this->ComplexEnum->getValue('ONE');
         $this->assertEquals('ONE', $oneValue->name);
@@ -444,7 +444,7 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('may be internally represented with complex values')
      */
-    public function testMayBeInternallyRepresentedWithComplexValues()
+    public function testMayBeInternallyRepresentedWithComplexValues() : void
     {
         $result = GraphQL::executeQuery($this->schema, '{
         first: complexEnum
@@ -473,13 +473,13 @@ class EnumTypeTest extends TestCase
     /**
      * @see it('can be introspected without error')
      */
-    public function testCanBeIntrospectedWithoutError()
+    public function testCanBeIntrospectedWithoutError() : void
     {
         $result = GraphQL::executeQuery($this->schema, Introspection::getIntrospectionQuery())->toArray();
         $this->assertArrayNotHasKey('errors', $result);
     }
 
-    public function testAllowsSimpleArrayAsValues()
+    public function testAllowsSimpleArrayAsValues() : void
     {
         $q = '{
             first: simpleEnum(fromName: "ONE")
diff --git a/tests/Type/IntrospectionTest.php b/tests/Type/IntrospectionTest.php
index 1eb3d95..b44a168 100644
--- a/tests/Type/IntrospectionTest.php
+++ b/tests/Type/IntrospectionTest.php
@@ -1171,9 +1171,8 @@ class IntrospectionTest extends TestCase
     /**
      * @see it('supports the __type root field')
      */
-    public function testSupportsThe__typeRootField()
+    public function testSupportsTheTypeRootField() : void
     {
-
         $TestType = new ObjectType([
             'name' => 'TestType',
             'fields' => [
@@ -1204,7 +1203,7 @@ class IntrospectionTest extends TestCase
     /**
      * @see it('identifies deprecated fields')
      */
-    public function testIdentifiesDeprecatedFields()
+    public function testIdentifiesDeprecatedFields() : void
     {
 
         $TestType = new ObjectType([
@@ -1259,7 +1258,7 @@ class IntrospectionTest extends TestCase
     /**
      * @see it('respects the includeDeprecated parameter for fields')
      */
-    public function testRespectsTheIncludeDeprecatedParameterForFields()
+    public function testRespectsTheIncludeDeprecatedParameterForFields() : void
     {
         $TestType = new ObjectType([
             'name' => 'TestType',
@@ -1324,7 +1323,7 @@ class IntrospectionTest extends TestCase
     /**
      * @see it('identifies deprecated enum values')
      */
-    public function testIdentifiesDeprecatedEnumValues()
+    public function testIdentifiesDeprecatedEnumValues() : void
     {
         $TestEnum = new EnumType([
             'name' => 'TestEnum',
@@ -1388,7 +1387,7 @@ class IntrospectionTest extends TestCase
     /**
      * @see it('respects the includeDeprecated parameter for enum values')
      */
-    public function testRespectsTheIncludeDeprecatedParameterForEnumValues()
+    public function testRespectsTheIncludeDeprecatedParameterForEnumValues() : void
     {
         $TestEnum = new EnumType([
             'name' => 'TestEnum',
@@ -1451,7 +1450,7 @@ class IntrospectionTest extends TestCase
     /**
      * @see it('fails as expected on the __type root field without an arg')
      */
-    public function testFailsAsExpectedOnThe__typeRootFieldWithoutAnArg()
+    public function testFailsAsExpectedOnTheTypeRootFieldWithoutAnArg() : void
     {
         $TestType = new ObjectType([
             'name' => 'TestType',
@@ -1483,7 +1482,7 @@ class IntrospectionTest extends TestCase
     /**
      * @see it('exposes descriptions on types and fields')
      */
-    public function testExposesDescriptionsOnTypesAndFields()
+    public function testExposesDescriptionsOnTypesAndFields() : void
     {
         $QueryRoot = new ObjectType([
             'name' => 'QueryRoot',
@@ -1543,7 +1542,7 @@ class IntrospectionTest extends TestCase
     /**
      * @see it('exposes descriptions on enums')
      */
-    public function testExposesDescriptionsOnEnums()
+    public function testExposesDescriptionsOnEnums() : void
     {
         $QueryRoot = new ObjectType([
             'name' => 'QueryRoot',
diff --git a/tests/Type/ResolutionTest.php b/tests/Type/ResolutionTest.php
index ac7c3c1..f4b0a72 100644
--- a/tests/Type/ResolutionTest.php
+++ b/tests/Type/ResolutionTest.php
@@ -275,7 +275,7 @@ class ResolutionTest extends TestCase
         ]);
     }
 
-    public function testEagerTypeResolution()
+    public function testEagerTypeResolution() : void
     {
         // Has internal types by default:
         $eagerTypeResolution = new EagerResolution([]);
@@ -460,7 +460,7 @@ class ResolutionTest extends TestCase
         $this->assertEquals($expectedDescriptor, $eagerTypeResolution->getDescriptor());
     }
 
-    public function testLazyResolutionFollowsEagerResolution()
+    public function testLazyResolutionFollowsEagerResolution() : void
     {
         // Lazy resolution should work the same way as eager resolution works, except that it should load types on demand
         $eager = new EagerResolution([]);
@@ -561,7 +561,7 @@ class ResolutionTest extends TestCase
         return $lazy;
     }
 
-    public function testLazyThrowsOnInvalidLoadedType()
+    public function testLazyThrowsOnInvalidLoadedType() : void
     {
         $lazy = $this->createLazy();
         $this->expectException(InvariantViolation::class);
@@ -569,7 +569,7 @@ class ResolutionTest extends TestCase
         $lazy->resolveType('int');
     }
 
-    public function testLazyThrowsOnInvalidLoadedPossibleType()
+    public function testLazyThrowsOnInvalidLoadedPossibleType() : void
     {
         $tmp = new InterfaceType(['name' => 'a', 'fields' => []]);
         $lazy = $this->createLazy();
@@ -578,7 +578,7 @@ class ResolutionTest extends TestCase
         $lazy->resolvePossibleTypes($tmp);
     }
 
-    public function testLazyThrowsOnInvalidLoadedPossibleTypeWithInteger()
+    public function testLazyThrowsOnInvalidLoadedPossibleTypeWithInteger() : void
     {
         $tmp = new InterfaceType(['name' => 'b', 'fields' => []]);
         $lazy = $this->createLazy();
diff --git a/tests/Type/ResolveInfoTest.php b/tests/Type/ResolveInfoTest.php
index d770a40..768f555 100644
--- a/tests/Type/ResolveInfoTest.php
+++ b/tests/Type/ResolveInfoTest.php
@@ -10,7 +10,7 @@ use PHPUnit\Framework\TestCase;
 
 class ResolveInfoTest extends TestCase
 {
-    public function testFieldSelection()
+    public function testFieldSelection() : void
     {
         $image = new ObjectType([
             'name' => 'Image',
@@ -164,7 +164,7 @@ class ResolveInfoTest extends TestCase
         $this->assertEquals($expectedDeepSelection, $actualDeepSelection);
     }
 
-    public function testMergedFragmentsFieldSelection()
+    public function testMergedFragmentsFieldSelection() : void
     {
         $image = new ObjectType([
             'name' => 'Image',
diff --git a/tests/Type/ScalarSerializationTest.php b/tests/Type/ScalarSerializationTest.php
index e4f512a..e26f0a1 100644
--- a/tests/Type/ScalarSerializationTest.php
+++ b/tests/Type/ScalarSerializationTest.php
@@ -12,7 +12,7 @@ class ScalarSerializationTest extends TestCase
     /**
      * @see it('serializes output int')
      */
-    public function testSerializesOutputInt()
+    public function testSerializesOutputInt() : void
     {
         $intType = Type::int();
 
@@ -26,7 +26,7 @@ class ScalarSerializationTest extends TestCase
         $this->assertSame(1, $intType->serialize(true));
     }
 
-    public function testSerializesOutputIntCannotRepresentFloat1()
+    public function testSerializesOutputIntCannotRepresentFloat1() : void
     {
         // The GraphQL specification does not allow serializing non-integer values
         // as Int to avoid accidental data loss.
@@ -36,7 +36,7 @@ class ScalarSerializationTest extends TestCase
         $intType->serialize(0.1);
     }
 
-    public function testSerializesOutputIntCannotRepresentFloat2()
+    public function testSerializesOutputIntCannotRepresentFloat2() : void
     {
         $intType = Type::int();
         $this->expectException(Error::class);
@@ -45,7 +45,7 @@ class ScalarSerializationTest extends TestCase
 
     }
 
-    public function testSerializesOutputIntCannotRepresentNegativeFloat()
+    public function testSerializesOutputIntCannotRepresentNegativeFloat() : void
     {
         $intType = Type::int();
         $this->expectException(Error::class);
@@ -54,7 +54,7 @@ class ScalarSerializationTest extends TestCase
 
     }
 
-    public function testSerializesOutputIntCannotRepresentNumericString()
+    public function testSerializesOutputIntCannotRepresentNumericString() : void
     {
         $intType = Type::int();
         $this->expectException(Error::class);
@@ -63,7 +63,7 @@ class ScalarSerializationTest extends TestCase
 
     }
 
-    public function testSerializesOutputIntCannotRepresentBiggerThan32Bits()
+    public function testSerializesOutputIntCannotRepresentBiggerThan32Bits() : void
     {
         // Maybe a safe PHP int, but bigger than 2^32, so not
         // representable as a GraphQL Int
@@ -74,7 +74,7 @@ class ScalarSerializationTest extends TestCase
 
     }
 
-    public function testSerializesOutputIntCannotRepresentLowerThan32Bits()
+    public function testSerializesOutputIntCannotRepresentLowerThan32Bits() : void
     {
         $intType = Type::int();
         $this->expectException(Error::class);
@@ -82,7 +82,7 @@ class ScalarSerializationTest extends TestCase
         $intType->serialize(-9876504321);
     }
 
-    public function testSerializesOutputIntCannotRepresentBiggerThanSigned32Bits()
+    public function testSerializesOutputIntCannotRepresentBiggerThanSigned32Bits() : void
     {
         $intType = Type::int();
         $this->expectException(Error::class);
@@ -90,7 +90,7 @@ class ScalarSerializationTest extends TestCase
         $intType->serialize(1e100);
     }
 
-    public function testSerializesOutputIntCannotRepresentLowerThanSigned32Bits()
+    public function testSerializesOutputIntCannotRepresentLowerThanSigned32Bits() : void
     {
         $intType = Type::int();
         $this->expectException(Error::class);
@@ -98,7 +98,7 @@ class ScalarSerializationTest extends TestCase
         $intType->serialize(-1e100);
     }
 
-    public function testSerializesOutputIntCannotRepresentString()
+    public function testSerializesOutputIntCannotRepresentString() : void
     {
         $intType = Type::int();
         $this->expectException(Error::class);
@@ -107,7 +107,7 @@ class ScalarSerializationTest extends TestCase
 
     }
 
-    public function testSerializesOutputIntCannotRepresentEmptyString()
+    public function testSerializesOutputIntCannotRepresentEmptyString() : void
     {
         $intType = Type::int();
         $this->expectException(Error::class);
@@ -118,7 +118,7 @@ class ScalarSerializationTest extends TestCase
     /**
      * @see it('serializes output float')
      */
-    public function testSerializesOutputFloat()
+    public function testSerializesOutputFloat() : void
     {
         $floatType = Type::float();
 
@@ -134,7 +134,7 @@ class ScalarSerializationTest extends TestCase
         $this->assertSame(1.0, $floatType->serialize(true));
     }
 
-    public function testSerializesOutputFloatCannotRepresentString()
+    public function testSerializesOutputFloatCannotRepresentString() : void
     {
         $floatType = Type::float();
         $this->expectException(Error::class);
@@ -142,7 +142,7 @@ class ScalarSerializationTest extends TestCase
         $floatType->serialize('one');
     }
 
-    public function testSerializesOutputFloatCannotRepresentEmptyString()
+    public function testSerializesOutputFloatCannotRepresentEmptyString() : void
     {
         $floatType = Type::float();
         $this->expectException(Error::class);
@@ -153,7 +153,7 @@ class ScalarSerializationTest extends TestCase
     /**
      * @see it('serializes output strings')
      */
-    public function testSerializesOutputStrings()
+    public function testSerializesOutputStrings() : void
     {
         $stringType = Type::string();
 
@@ -166,7 +166,7 @@ class ScalarSerializationTest extends TestCase
         $this->assertSame('2', $stringType->serialize(new ObjectIdStub(2)));
     }
 
-    public function testSerializesOutputStringsCannotRepresentArray()
+    public function testSerializesOutputStringsCannotRepresentArray() : void
     {
         $stringType = Type::string();
         $this->expectException(Error::class);
@@ -174,7 +174,7 @@ class ScalarSerializationTest extends TestCase
         $stringType->serialize([]);
     }
 
-    public function testSerializesOutputStringsCannotRepresentObject()
+    public function testSerializesOutputStringsCannotRepresentObject() : void
     {
         $stringType = Type::string();
         $this->expectException(Error::class);
@@ -185,7 +185,7 @@ class ScalarSerializationTest extends TestCase
     /**
      * @see it('serializes output boolean')
      */
-    public function testSerializesOutputBoolean()
+    public function testSerializesOutputBoolean() : void
     {
         $boolType = Type::boolean();
 
@@ -200,7 +200,7 @@ class ScalarSerializationTest extends TestCase
         // TODO: how should it behave on '0'?
     }
 
-    public function testSerializesOutputID()
+    public function testSerializesOutputID() : void
     {
         $idType = Type::id();
 
@@ -214,7 +214,7 @@ class ScalarSerializationTest extends TestCase
         $this->assertSame('2', $idType->serialize(new ObjectIdStub(2)));
     }
 
-    public function testSerializesOutputIDCannotRepresentObject()
+    public function testSerializesOutputIDCannotRepresentObject() : void
     {
         $idType = Type::id();
         $this->expectException(Error::class);
diff --git a/tests/Type/SchemaTest.php b/tests/Type/SchemaTest.php
index fc354b1..7224622 100644
--- a/tests/Type/SchemaTest.php
+++ b/tests/Type/SchemaTest.php
@@ -93,7 +93,7 @@ class SchemaTest extends TestCase
     /**
      * @see it('throws human-reable error if schema.types is not defined')
      */
-    public function testThrowsHumanReableErrorIfSchemaTypesIsNotDefined()
+    public function testThrowsHumanReableErrorIfSchemaTypesIsNotDefined() : void
     {
         $this->markTestSkipped("Can't check interface implementations without full schema scan");
 
@@ -111,7 +111,7 @@ class SchemaTest extends TestCase
     /**
      * @see it('includes input types only used in directives')
      */
-    public function testIncludesInputTypesOnlyUsedInDirectives()
+    public function testIncludesInputTypesOnlyUsedInDirectives() : void
     {
         $typeMap = $this->schema->getTypeMap();
         $this->assertArrayHasKey('DirInput', $typeMap);
diff --git a/tests/Type/TypeLoaderTest.php b/tests/Type/TypeLoaderTest.php
index a1c0233..1893ca7 100644
--- a/tests/Type/TypeLoaderTest.php
+++ b/tests/Type/TypeLoaderTest.php
@@ -151,7 +151,7 @@ class TypeLoaderTest extends TestCase
         };
     }
 
-    public function testSchemaAcceptsTypeLoader()
+    public function testSchemaAcceptsTypeLoader() : void
     {
         $this->expectNotToPerformAssertions();
         new Schema([
@@ -163,7 +163,7 @@ class TypeLoaderTest extends TestCase
         ]);
     }
 
-    public function testSchemaRejectsNonCallableTypeLoader()
+    public function testSchemaRejectsNonCallableTypeLoader() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage('Schema type loader must be callable if provided but got: []');
@@ -177,7 +177,7 @@ class TypeLoaderTest extends TestCase
         ]);
     }
 
-    public function testWorksWithoutTypeLoader()
+    public function testWorksWithoutTypeLoader() : void
     {
         $schema = new Schema([
             'query' => $this->query,
@@ -215,7 +215,7 @@ class TypeLoaderTest extends TestCase
         $this->assertArraySubset($expectedTypeMap, $schema->getTypeMap());
     }
 
-    public function testWorksWithTypeLoader()
+    public function testWorksWithTypeLoader() : void
     {
         $schema = new Schema([
             'query' => $this->query,
@@ -241,7 +241,7 @@ class TypeLoaderTest extends TestCase
         $this->assertEquals(['Node', 'Content', 'PostStoryMutationInput'], $this->calls);
     }
 
-    public function testOnlyCallsLoaderOnce()
+    public function testOnlyCallsLoaderOnce() : void
     {
         $schema = new Schema([
             'query' => $this->query,
@@ -255,7 +255,7 @@ class TypeLoaderTest extends TestCase
         $this->assertEquals(['Node'], $this->calls);
     }
 
-    public function testFailsOnNonExistentType()
+    public function testFailsOnNonExistentType() : void
     {
         $schema = new Schema([
             'query' => $this->query,
@@ -268,7 +268,7 @@ class TypeLoaderTest extends TestCase
         $schema->getType('NonExistingType');
     }
 
-    public function testFailsOnNonType()
+    public function testFailsOnNonType() : void
     {
         $schema = new Schema([
             'query' => $this->query,
@@ -283,7 +283,7 @@ class TypeLoaderTest extends TestCase
         $schema->getType('Node');
     }
 
-    public function testFailsOnInvalidLoad()
+    public function testFailsOnInvalidLoad() : void
     {
         $schema = new Schema([
             'query' => $this->query,
@@ -298,7 +298,7 @@ class TypeLoaderTest extends TestCase
         $schema->getType('Node');
     }
 
-    public function testPassesThroughAnExceptionInLoader()
+    public function testPassesThroughAnExceptionInLoader() : void
     {
         $schema = new Schema([
             'query' => $this->query,
@@ -313,7 +313,7 @@ class TypeLoaderTest extends TestCase
         $schema->getType('Node');
     }
 
-    public function testReturnsIdenticalResults()
+    public function testReturnsIdenticalResults() : void
     {
         $withoutLoader = new Schema([
             'query' => $this->query,
@@ -332,7 +332,7 @@ class TypeLoaderTest extends TestCase
         $this->assertSame($withoutLoader->getDirectives(), $withLoader->getDirectives());
     }
 
-    public function testSkipsLoaderForInternalTypes()
+    public function testSkipsLoaderForInternalTypes() : void
     {
         $schema = new Schema([
             'query' => $this->query,
diff --git a/tests/Type/ValidationTest.php b/tests/Type/ValidationTest.php
index 8fd4823..d388bb5 100644
--- a/tests/Type/ValidationTest.php
+++ b/tests/Type/ValidationTest.php
@@ -145,7 +145,7 @@ class ValidationTest extends TestCase
         }
     }
 
-    public function testRejectsTypesWithoutNames()
+    public function testRejectsTypesWithoutNames() : void
     {
         $this->assertEachCallableThrows([
             function() {
@@ -171,7 +171,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts a Schema whose query type is an object type')
      */
-    public function testAcceptsASchemaWhoseQueryTypeIsAnObjectType()
+    public function testAcceptsASchemaWhoseQueryTypeIsAnObjectType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -194,7 +194,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts a Schema whose query and mutation types are object types')
      */
-    public function testAcceptsASchemaWhoseQueryAndMutationTypesAreObjectTypes()
+    public function testAcceptsASchemaWhoseQueryAndMutationTypesAreObjectTypes() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -227,7 +227,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts a Schema whose query and subscription types are object types')
      */
-    public function testAcceptsASchemaWhoseQueryAndSubscriptionTypesAreObjectTypes()
+    public function testAcceptsASchemaWhoseQueryAndSubscriptionTypesAreObjectTypes() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -260,7 +260,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a Schema without a query type')
      */
-    public function testRejectsASchemaWithoutAQueryType()
+    public function testRejectsASchemaWithoutAQueryType() : void
     {
         $schema = BuildSchema::build('
       type Mutation {
@@ -296,7 +296,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a Schema whose query root type is not an Object type')
      */
-    public function testRejectsASchemaWhoseQueryTypeIsNotAnObjectType()
+    public function testRejectsASchemaWhoseQueryTypeIsNotAnObjectType() : void
     {
         $schema = BuildSchema::build('
       input Query {
@@ -335,7 +335,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a Schema whose mutation type is an input type')
      */
-    public function testRejectsASchemaWhoseMutationTypeIsAnInputType()
+    public function testRejectsASchemaWhoseMutationTypeIsAnInputType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -382,7 +382,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a Schema whose subscription type is an input type')
      */
-    public function testRejectsASchemaWhoseSubscriptionTypeIsAnInputType()
+    public function testRejectsASchemaWhoseSubscriptionTypeIsAnInputType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -431,7 +431,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a Schema whose directives are incorrectly typed')
      */
-    public function testRejectsASchemaWhoseDirectivesAreIncorrectlyTyped()
+    public function testRejectsASchemaWhoseDirectivesAreIncorrectlyTyped() : void
     {
         $schema = new Schema([
             'query' => $this->SomeObjectType,
@@ -449,7 +449,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an Object type with fields object')
      */
-    public function testAcceptsAnObjectTypeWithFieldsObject()
+    public function testAcceptsAnObjectTypeWithFieldsObject() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -467,7 +467,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object type with missing fields')
      */
-    public function testRejectsAnObjectTypeWithMissingFields()
+    public function testRejectsAnObjectTypeWithMissingFields() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -513,7 +513,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object type with incorrectly named fields')
      */
-    public function testRejectsAnObjectTypeWithIncorrectlyNamedFields()
+    public function testRejectsAnObjectTypeWithIncorrectlyNamedFields() : void
     {
         $schema = $this->schemaWithFieldType(
             new ObjectType([
@@ -533,7 +533,7 @@ class ValidationTest extends TestCase
         );
     }
 
-    public function testAcceptsShorthandNotationForFields()
+    public function testAcceptsShorthandNotationForFields() : void
     {
         $this->expectNotToPerformAssertions();
         $schema = $this->schemaWithFieldType(
@@ -552,7 +552,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts field args with valid names')
      */
-    public function testAcceptsFieldArgsWithValidNames()
+    public function testAcceptsFieldArgsWithValidNames() : void
     {
         $schema = $this->schemaWithFieldType(new ObjectType([
             'name' => 'SomeObject',
@@ -571,7 +571,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects field arg with invalid names')
      */
-    public function testRejectsFieldArgWithInvalidNames()
+    public function testRejectsFieldArgWithInvalidNames() : void
     {
         $QueryType = new ObjectType([
             'name' => 'SomeObject',
@@ -597,7 +597,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts a Union type with member types')
      */
-    public function testAcceptsAUnionTypeWithArrayTypes()
+    public function testAcceptsAUnionTypeWithArrayTypes() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -623,7 +623,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a Union type with empty types')
      */
-    public function testRejectsAUnionTypeWithEmptyTypes()
+    public function testRejectsAUnionTypeWithEmptyTypes() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -644,7 +644,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a Union type with duplicated member type')
      */
-    public function testRejectsAUnionTypeWithDuplicatedMemberType()
+    public function testRejectsAUnionTypeWithDuplicatedMemberType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -676,7 +676,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a Union type with non-Object members types')
      */
-    public function testRejectsAUnionTypeWithNonObjectMembersType()
+    public function testRejectsAUnionTypeWithNonObjectMembersType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -735,7 +735,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an Input Object type with fields')
      */
-    public function testAcceptsAnInputObjectTypeWithFields()
+    public function testAcceptsAnInputObjectTypeWithFields() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -752,7 +752,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Input Object type with missing fields')
      */
-    public function testRejectsAnInputObjectTypeWithMissingFields()
+    public function testRejectsAnInputObjectTypeWithMissingFields() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -773,7 +773,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Input Object type with incorrectly typed fields')
      */
-    public function testRejectsAnInputObjectTypeWithIncorrectlyTypedFields()
+    public function testRejectsAnInputObjectTypeWithIncorrectlyTypedFields() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -809,7 +809,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Enum type without values')
      */
-    public function testRejectsAnEnumTypeWithoutValues()
+    public function testRejectsAnEnumTypeWithoutValues() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -830,7 +830,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Enum type with duplicate values')
      */
-    public function testRejectsAnEnumTypeWithDuplicateValues()
+    public function testRejectsAnEnumTypeWithDuplicateValues() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -851,7 +851,7 @@ class ValidationTest extends TestCase
         );
     }
 
-    public function testDoesNotAllowIsDeprecatedWithoutDeprecationReasonOnEnum()
+    public function testDoesNotAllowIsDeprecatedWithoutDeprecationReasonOnEnum() : void
     {
         $enum = new EnumType([
             'name' => 'SomeEnum',
@@ -892,7 +892,7 @@ class ValidationTest extends TestCase
      * @see it('rejects an Enum type with incorrectly named values')
      * @dataProvider invalidEnumValueName
      */
-    public function testRejectsAnEnumTypeWithIncorrectlyNamedValues($name, $expectedMessage)
+    public function testRejectsAnEnumTypeWithIncorrectlyNamedValues($name, $expectedMessage) : void
     {
         $schema = $this->schemaWithEnum($name);
 
@@ -909,7 +909,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an output type as an Object field type')
      */
-    public function testAcceptsAnOutputTypeAsNnObjectFieldType()
+    public function testAcceptsAnOutputTypeAsNnObjectFieldType() : void
     {
         foreach ($this->outputTypes as $type) {
             $schema = $this->schemaWithObjectFieldOfType($type);
@@ -920,7 +920,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an empty Object field type')
      */
-    public function testRejectsAnEmptyObjectFieldType()
+    public function testRejectsAnEmptyObjectFieldType() : void
     {
         $schema = $this->schemaWithObjectFieldOfType(null);
 
@@ -935,7 +935,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a non-output type as an Object field type')
      */
-    public function testRejectsANonOutputTypeAsAnObjectFieldType()
+    public function testRejectsANonOutputTypeAsAnObjectFieldType() : void
     {
         foreach ($this->notOutputTypes as $type) {
             $schema = $this->schemaWithObjectFieldOfType($type);
@@ -952,7 +952,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects with relevant locations for a non-output type as an Object field type')
      */
-    public function testRejectsWithReleventLocationsForANonOutputTypeAsAnObjectFieldType()
+    public function testRejectsWithReleventLocationsForANonOutputTypeAsAnObjectFieldType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -977,7 +977,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object implementing a non-type values')
      */
-    public function testRejectsAnObjectImplementingANonTypeValues()
+    public function testRejectsAnObjectImplementingANonTypeValues() : void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -999,7 +999,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object implementing a non-Interface type')
      */
-    public function testRejectsAnObjectImplementingANonInterfaceType()
+    public function testRejectsAnObjectImplementingANonInterfaceType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1026,7 +1026,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object implementing the same interface twice')
      */
-    public function testRejectsAnObjectImplementingTheSameInterfaceTwice()
+    public function testRejectsAnObjectImplementingTheSameInterfaceTwice() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1053,7 +1053,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object implementing the same interface twice due to extension')
      */
-    public function testRejectsAnObjectImplementingTheSameInterfaceTwiceDueToExtension()
+    public function testRejectsAnObjectImplementingTheSameInterfaceTwiceDueToExtension() : void
     {
         $this->expectNotToPerformAssertions();
         $this->markTestIncomplete('extend does not work this way (yet).');
@@ -1086,7 +1086,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an output type as an Interface field type')
      */
-    public function testAcceptsAnOutputTypeAsAnInterfaceFieldType()
+    public function testAcceptsAnOutputTypeAsAnInterfaceFieldType() : void
     {
         foreach ($this->outputTypes as $type) {
             $schema = $this->schemaWithInterfaceFieldOfType($type);
@@ -1097,7 +1097,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an empty Interface field type')
      */
-    public function testRejectsAnEmptyInterfaceFieldType()
+    public function testRejectsAnEmptyInterfaceFieldType() : void
     {
         $schema = $this->schemaWithInterfaceFieldOfType(null);
         $this->assertContainsValidationMessage(
@@ -1111,7 +1111,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a non-output type as an Interface field type')
      */
-    public function testRejectsANonOutputTypeAsAnInterfaceFieldType()
+    public function testRejectsANonOutputTypeAsAnInterfaceFieldType() : void
     {
         foreach ($this->notOutputTypes as $type) {
             $schema = $this->schemaWithInterfaceFieldOfType($type);
@@ -1128,7 +1128,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a non-output type as an Interface field type with locations')
      */
-    public function testRejectsANonOutputTypeAsAnInterfaceFieldTypeWithLocations()
+    public function testRejectsANonOutputTypeAsAnInterfaceFieldTypeWithLocations() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1157,7 +1157,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an input type as a field arg type')
      */
-    public function testAcceptsAnInputTypeAsAFieldArgType()
+    public function testAcceptsAnInputTypeAsAFieldArgType() : void
     {
         foreach ($this->inputTypes as $type) {
             $schema = $this->schemaWithArgOfType($type);
@@ -1168,7 +1168,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an empty field arg type')
      */
-    public function testRejectsAnEmptyFieldArgType()
+    public function testRejectsAnEmptyFieldArgType() : void
     {
         $schema = $this->schemaWithArgOfType(null);
         $this->assertContainsValidationMessage(
@@ -1182,7 +1182,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a non-input type as a field arg type')
      */
-    public function testRejectsANonInputTypeAsAFieldArgType()
+    public function testRejectsANonInputTypeAsAFieldArgType() : void
     {
         foreach ($this->notInputTypes as $type) {
             $schema = $this->schemaWithArgOfType($type);
@@ -1198,7 +1198,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a non-input type as a field arg with locations')
      */
-    public function testANonInputTypeAsAFieldArgWithLocations()
+    public function testANonInputTypeAsAFieldArgWithLocations() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1223,7 +1223,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an input type as an input field type')
      */
-    public function testAcceptsAnInputTypeAsAnInputFieldType()
+    public function testAcceptsAnInputTypeAsAnInputFieldType() : void
     {
         foreach ($this->inputTypes as $type) {
             $schema = $this->schemaWithInputFieldOfType($type);
@@ -1234,7 +1234,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an empty input field type')
      */
-    public function testRejectsAnEmptyInputFieldType()
+    public function testRejectsAnEmptyInputFieldType() : void
     {
         $schema = $this->schemaWithInputFieldOfType(null);
         $this->assertContainsValidationMessage(
@@ -1248,7 +1248,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a non-input type as an input field type')
      */
-    public function testRejectsANonInputTypeAsAnInputFieldType()
+    public function testRejectsANonInputTypeAsAnInputFieldType() : void
     {
         foreach ($this->notInputTypes as $type) {
             $schema = $this->schemaWithInputFieldOfType($type);
@@ -1264,7 +1264,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects a non-input type as an input object field with locations')
      */
-    public function testRejectsANonInputTypeAsAnInputObjectFieldWithLocations()
+    public function testRejectsANonInputTypeAsAnInputObjectFieldWithLocations() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1293,7 +1293,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an Object which implements an Interface')
      */
-    public function testAcceptsAnObjectWhichImplementsAnInterface()
+    public function testAcceptsAnObjectWhichImplementsAnInterface() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1318,7 +1318,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an Object which implements an Interface along with more fields')
      */
-    public function testAcceptsAnObjectWhichImplementsAnInterfaceAlongWithMoreFields()
+    public function testAcceptsAnObjectWhichImplementsAnInterfaceAlongWithMoreFields() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1344,7 +1344,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an Object which implements an Interface field along with additional optional arguments')
      */
-    public function testAcceptsAnObjectWhichImplementsAnInterfaceFieldAlongWithAdditionalOptionalArguments()
+    public function testAcceptsAnObjectWhichImplementsAnInterfaceFieldAlongWithAdditionalOptionalArguments() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1369,7 +1369,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object missing an Interface field')
      */
-    public function testRejectsAnObjectMissingAnInterfaceField()
+    public function testRejectsAnObjectMissingAnInterfaceField() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1398,7 +1398,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object with an incorrectly typed Interface field')
      */
-    public function testRejectsAnObjectWithAnIncorrectlyTypedInterfaceField()
+    public function testRejectsAnObjectWithAnIncorrectlyTypedInterfaceField() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1427,7 +1427,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object with a differently typed Interface field')
      */
-    public function testRejectsAnObjectWithADifferentlyTypedInterfaceField()
+    public function testRejectsAnObjectWithADifferentlyTypedInterfaceField() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1459,7 +1459,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an Object with a subtyped Interface field (interface)')
      */
-    public function testAcceptsAnObjectWithASubtypedInterfaceFieldForInterface()
+    public function testAcceptsAnObjectWithASubtypedInterfaceFieldForInterface() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1481,7 +1481,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an Object with a subtyped Interface field (union)')
      */
-    public function testAcceptsAnObjectWithASubtypedInterfaceFieldForUnion()
+    public function testAcceptsAnObjectWithASubtypedInterfaceFieldForUnion() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1509,7 +1509,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object missing an Interface argument')
      */
-    public function testRejectsAnObjectMissingAnInterfaceArgument()
+    public function testRejectsAnObjectMissingAnInterfaceArgument() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1538,7 +1538,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object with an incorrectly typed Interface argument')
      */
-    public function testRejectsAnObjectWithAnIncorrectlyTypedInterfaceArgument()
+    public function testRejectsAnObjectWithAnIncorrectlyTypedInterfaceArgument() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1567,7 +1567,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object with both an incorrectly typed field and argument')
      */
-    public function testRejectsAnObjectWithBothAnIncorrectlyTypedFieldAndArgument()
+    public function testRejectsAnObjectWithBothAnIncorrectlyTypedFieldAndArgument() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1600,7 +1600,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object which implements an Interface field along with additional required arguments')
      */
-    public function testRejectsAnObjectWhichImplementsAnInterfaceFieldAlongWithAdditionalRequiredArguments()
+    public function testRejectsAnObjectWhichImplementsAnInterfaceFieldAlongWithAdditionalRequiredArguments() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1630,7 +1630,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an Object with an equivalently wrapped Interface field type')
      */
-    public function testAcceptsAnObjectWithAnEquivalentlyWrappedInterfaceFieldType()
+    public function testAcceptsAnObjectWithAnEquivalentlyWrappedInterfaceFieldType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1652,7 +1652,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object with a non-list Interface field list type')
      */
-    public function testRejectsAnObjectWithANonListInterfaceFieldListType()
+    public function testRejectsAnObjectWithANonListInterfaceFieldListType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1681,7 +1681,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object with a list Interface field non-list type')
      */
-    public function testRejectsAnObjectWithAListInterfaceFieldNonListType()
+    public function testRejectsAnObjectWithAListInterfaceFieldNonListType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1710,7 +1710,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('accepts an Object with a subset non-null Interface field type')
      */
-    public function testAcceptsAnObjectWithASubsetNonNullInterfaceFieldType()
+    public function testAcceptsAnObjectWithASubsetNonNullInterfaceFieldType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1732,7 +1732,7 @@ class ValidationTest extends TestCase
     /**
      * @see it('rejects an Object with a superset nullable Interface field type')
      */
-    public function testRejectsAnObjectWithASupersetNullableInterfaceFieldType()
+    public function testRejectsAnObjectWithASupersetNullableInterfaceFieldType() : void
     {
         $schema = BuildSchema::build('
       type Query {
@@ -1758,7 +1758,7 @@ class ValidationTest extends TestCase
         );
     }
 
-    public function testRejectsDifferentInstancesOfTheSameType()
+    public function testRejectsDifferentInstancesOfTheSameType() : void
     {
         // Invalid: always creates new instance vs returning one from registry
         $typeLoader = function($name) use (&$typeLoader) {
diff --git a/tests/Utils/AssertValidNameTest.php b/tests/Utils/AssertValidNameTest.php
index 81e3010..87fbfea 100644
--- a/tests/Utils/AssertValidNameTest.php
+++ b/tests/Utils/AssertValidNameTest.php
@@ -13,7 +13,7 @@ class AssertValidNameTest extends TestCase
     /**
      * @see it('throws for use of leading double underscores')
      */
-    public function testThrowsForUseOfLeadingDoubleUnderscores()
+    public function testThrowsForUseOfLeadingDoubleUnderscores() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('"__bad" must not begin with "__", which is reserved by GraphQL introspection.');
@@ -23,7 +23,7 @@ class AssertValidNameTest extends TestCase
     /**
      * @see it('throws for non-strings')
      */
-    public function testThrowsForNonStrings()
+    public function testThrowsForNonStrings() : void
     {
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage('Expected string');
@@ -33,7 +33,7 @@ class AssertValidNameTest extends TestCase
     /**
      * @see it('throws for names with invalid characters')
      */
-    public function testThrowsForNamesWithInvalidCharacters()
+    public function testThrowsForNamesWithInvalidCharacters() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Names must match');
diff --git a/tests/Utils/AstFromValueTest.php b/tests/Utils/AstFromValueTest.php
index ddeb698..777dddb 100644
--- a/tests/Utils/AstFromValueTest.php
+++ b/tests/Utils/AstFromValueTest.php
@@ -24,7 +24,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts boolean values to ASTs')
      */
-    public function testConvertsBooleanValueToASTs()
+    public function testConvertsBooleanValueToASTs() : void
     {
         $this->assertEquals(new BooleanValueNode(['value' => true]), AST::astFromValue(true, Type::boolean()));
         $this->assertEquals(new BooleanValueNode(['value' => false]), AST::astFromValue(false, Type::boolean()));
@@ -38,7 +38,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts Int values to Int ASTs')
      */
-    public function testConvertsIntValuesToASTs()
+    public function testConvertsIntValuesToASTs() : void
     {
         $this->assertEquals(new IntValueNode(['value' => '-1']), AST::astFromValue(-1, Type::int()));
         $this->assertEquals(new IntValueNode(['value' => '123']), AST::astFromValue(123.0, Type::int()));
@@ -46,7 +46,7 @@ class AstFromValueTest extends TestCase
         $this->assertEquals(new IntValueNode(['value' => '0']), AST::astFromValue(0e4, Type::int()));
     }
 
-    public function testConvertsIntValuesToASTsCannotRepresentNonInteger()
+    public function testConvertsIntValuesToASTsCannotRepresentNonInteger() : void
     {
         // GraphQL spec does not allow coercing non-integer values to Int to avoid
         // accidental data loss.
@@ -55,7 +55,7 @@ class AstFromValueTest extends TestCase
         AST::astFromValue(123.5, Type::int());
     }
 
-    public function testConvertsIntValuesToASTsCannotRepresentNon32bitsInteger()
+    public function testConvertsIntValuesToASTsCannotRepresentNon32bitsInteger() : void
     {
         $this->expectException(\Throwable::class);
         $this->expectExceptionMessage('Int cannot represent non 32-bit signed integer value: 1.0E+40');
@@ -65,7 +65,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts Float values to Int/Float ASTs')
      */
-    public function testConvertsFloatValuesToIntOrFloatASTs()
+    public function testConvertsFloatValuesToIntOrFloatASTs() : void
     {
         $this->assertEquals(new IntValueNode(['value' => '-1']), AST::astFromValue(-1, Type::float()));
         $this->assertEquals(new IntValueNode(['value' => '123']), AST::astFromValue(123, Type::float()));
@@ -79,7 +79,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts String values to String ASTs')
      */
-    public function testConvertsStringValuesToASTs()
+    public function testConvertsStringValuesToASTs() : void
     {
         $this->assertEquals(new StringValueNode(['value' => 'hello']), AST::astFromValue('hello', Type::string()));
         $this->assertEquals(new StringValueNode(['value' => 'VALUE']), AST::astFromValue('VALUE', Type::string()));
@@ -93,7 +93,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts ID values to Int/String ASTs')
      */
-    public function testConvertIdValuesToIntOrStringASTs()
+    public function testConvertIdValuesToIntOrStringASTs() : void
     {
         $this->assertEquals(new StringValueNode(['value' => 'hello']), AST::astFromValue('hello', Type::id()));
         $this->assertEquals(new StringValueNode(['value' => 'VALUE']), AST::astFromValue('VALUE', Type::id()));
@@ -110,7 +110,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('does not converts NonNull values to NullValue')
      */
-    public function testDoesNotConvertsNonNullValuestoNullValue()
+    public function testDoesNotConvertsNonNullValuestoNullValue() : void
     {
         $this->assertSame(null, AST::astFromValue(null, Type::nonNull(Type::boolean())));
     }
@@ -118,7 +118,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts string values to Enum ASTs if possible')
      */
-    public function testConvertsStringValuesToEnumASTsIfPossible()
+    public function testConvertsStringValuesToEnumASTsIfPossible() : void
     {
         $this->assertEquals(new EnumValueNode(['value' => 'HELLO']), AST::astFromValue('HELLO', $this->myEnum()));
         $this->assertEquals(new EnumValueNode(['value' => 'COMPLEX']), AST::astFromValue($this->complexValue(), $this->myEnum()));
@@ -133,7 +133,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts array values to List ASTs')
      */
-    public function testConvertsArrayValuesToListASTs()
+    public function testConvertsArrayValuesToListASTs() : void
     {
         $value1 = new ListValueNode([
             'values' => [
@@ -155,7 +155,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts list singletons')
      */
-    public function testConvertsListSingletons()
+    public function testConvertsListSingletons() : void
     {
         $this->assertEquals(new StringValueNode(['value' => 'FOO']), AST::astFromValue('FOO', Type::listOf(Type::string())));
     }
@@ -163,7 +163,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts input objects')
      */
-    public function testConvertsInputObjects()
+    public function testConvertsInputObjects() : void
     {
         $inputObj = new InputObjectType([
             'name' => 'MyInputObj',
@@ -188,7 +188,7 @@ class AstFromValueTest extends TestCase
     /**
      * @see it('converts input objects with explicit nulls')
      */
-    public function testConvertsInputObjectsWithExplicitNulls()
+    public function testConvertsInputObjectsWithExplicitNulls() : void
     {
         $inputObj = new InputObjectType([
             'name' => 'MyInputObj',
diff --git a/tests/Utils/AstFromValueUntypedTest.php b/tests/Utils/AstFromValueUntypedTest.php
index 790156d..eb168cf 100644
--- a/tests/Utils/AstFromValueUntypedTest.php
+++ b/tests/Utils/AstFromValueUntypedTest.php
@@ -19,7 +19,7 @@ class AstFromValueUntypedTest extends TestCase
     /**
      * @see it('parses simple values')
      */
-    public function testParsesSimpleValues()
+    public function testParsesSimpleValues() : void
     {
         $this->assertTestCase('null', null);
         $this->assertTestCase('true', true);
@@ -32,7 +32,7 @@ class AstFromValueUntypedTest extends TestCase
     /**
      * @see it('parses lists of values')
      */
-    public function testParsesListsOfValues()
+    public function testParsesListsOfValues() : void
     {
         $this->assertTestCase('[true, false]', [true, false]);
         $this->assertTestCase('[true, 123.45]', [true, 123.45]);
@@ -43,7 +43,7 @@ class AstFromValueUntypedTest extends TestCase
     /**
      * @see it('parses input objects')
      */
-    public function testParsesInputObjects()
+    public function testParsesInputObjects() : void
     {
         $this->assertTestCase(
             '{ int: 123, bool: false }',
@@ -59,7 +59,7 @@ class AstFromValueUntypedTest extends TestCase
     /**
      * @see it('parses enum values as plain strings')
      */
-    public function testParsesEnumValuesAsPlainStrings()
+    public function testParsesEnumValuesAsPlainStrings() : void
     {
         $this->assertTestCase(
             'TEST_ENUM_VALUE',
@@ -75,7 +75,7 @@ class AstFromValueUntypedTest extends TestCase
     /**
      * @see it('parses enum values as plain strings')
      */
-    public function testParsesVariables()
+    public function testParsesVariables() : void
     {
         $this->assertTestCase(
             '$testVariable',
diff --git a/tests/Utils/BreakingChangesFinderTest.php b/tests/Utils/BreakingChangesFinderTest.php
index 11eb466..37f575d 100644
--- a/tests/Utils/BreakingChangesFinderTest.php
+++ b/tests/Utils/BreakingChangesFinderTest.php
@@ -36,7 +36,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a type was removed or not')
      */
-    public function testShouldDetectIfTypeWasRemovedOrNot()
+    public function testShouldDetectIfTypeWasRemovedOrNot() : void
     {
         $type1 = new ObjectType([
             'name' => 'Type1',
@@ -77,7 +77,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a type changed its type')
      */
-    public function testShouldDetectIfATypeChangedItsType()
+    public function testShouldDetectIfATypeChangedItsType() : void
     {
         $objectType = new ObjectType([
             'name' => 'ObjectType',
@@ -124,7 +124,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a field on a type was deleted or changed type')
      */
-    public function testShouldDetectIfAFieldOnATypeWasDeletedOrChangedType()
+    public function testShouldDetectIfAFieldOnATypeWasDeletedOrChangedType() : void
     {
         $typeA = new ObjectType([
             'name' => 'TypeA',
@@ -268,7 +268,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if fields on input types changed kind or were removed')
      */
-    public function testShouldDetectIfFieldsOnInputTypesChangedKindOrWereRemoved()
+    public function testShouldDetectIfFieldsOnInputTypesChangedKindOrWereRemoved() : void
     {
         $oldInputType = new InputObjectType([
             'name' => 'InputType1',
@@ -432,7 +432,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a non-null field is added to an input type')
      */
-    public function testShouldDetectIfANonNullFieldIsAddedToAnInputType()
+    public function testShouldDetectIfANonNullFieldIsAddedToAnInputType() : void
     {
         $oldInputType = new InputObjectType([
             'name' => 'InputType1',
@@ -476,7 +476,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a type was removed from a union type')
      */
-    public function testShouldRetectIfATypeWasRemovedFromAUnionType()
+    public function testShouldRetectIfATypeWasRemovedFromAUnionType() : void
     {
         $type1 = new ObjectType([
             'name' => 'Type1',
@@ -539,7 +539,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a value was removed from an enum type')
      */
-    public function testShouldDetectIfAValueWasRemovedFromAnEnumType()
+    public function testShouldDetectIfAValueWasRemovedFromAnEnumType() : void
     {
         $oldEnumType = new EnumType([
             'name' => 'EnumType1',
@@ -584,7 +584,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a field argument was removed')
      */
-    public function testShouldDetectIfAFieldArgumentWasRemoved()
+    public function testShouldDetectIfAFieldArgumentWasRemoved() : void
     {
         $oldType = new ObjectType([
             'name' => 'Type1',
@@ -666,7 +666,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a field argument has changed type')
      */
-    public function testShouldDetectIfAFieldArgumentHasChangedType()
+    public function testShouldDetectIfAFieldArgumentHasChangedType() : void
     {
         $oldType = new ObjectType([
             'name' => 'Type1',
@@ -787,7 +787,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a non-null field argument was added')
      */
-    public function testShouldDetectIfANonNullFieldArgumentWasAdded()
+    public function testShouldDetectIfANonNullFieldArgumentWasAdded() : void
     {
         $oldType = new ObjectType([
             'name' => 'Type1',
@@ -836,7 +836,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should not flag args with the same type signature as breaking')
      */
-    public function testShouldNotFlagArgsWithTheSameTypeSignatureAsBreaking()
+    public function testShouldNotFlagArgsWithTheSameTypeSignatureAsBreaking() : void
     {
         $inputType1a = new InputObjectType([
             'name' => 'InputType1',
@@ -893,7 +893,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should consider args that move away from NonNull as non-breaking')
      */
-    public function testShouldConsiderArgsThatMoveAwayFromNonNullAsNonBreaking()
+    public function testShouldConsiderArgsThatMoveAwayFromNonNullAsNonBreaking() : void
     {
         $oldType = new ObjectType([
             'name' => 'Type1',
@@ -933,7 +933,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect interfaces removed from types')
      */
-    public function testShouldDetectInterfacesRemovedFromTypes()
+    public function testShouldDetectInterfacesRemovedFromTypes() : void
     {
         $interface1 = new InterfaceType([
             'name' => 'Interface1',
@@ -980,7 +980,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect all breaking changes')
      */
-    public function testShouldDetectAllBreakingChanges()
+    public function testShouldDetectAllBreakingChanges() : void
     {
         $typeThatGetsRemoved = new ObjectType([
             'name' => 'TypeThatGetsRemoved',
@@ -1246,7 +1246,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a directive was explicitly removed')
      */
-    public function testShouldDetectIfADirectiveWasExplicitlyRemoved()
+    public function testShouldDetectIfADirectiveWasExplicitlyRemoved() : void
     {
         $oldSchema = new Schema([
             'directives' => [Directive::skipDirective(), Directive::includeDirective()],
@@ -1271,7 +1271,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a directive was implicitly removed')
      */
-    public function testShouldDetectIfADirectiveWasImplicitlyRemoved()
+    public function testShouldDetectIfADirectiveWasImplicitlyRemoved() : void
     {
         $oldSchema = new Schema([]);
 
@@ -1294,7 +1294,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a directive argument was removed')
      */
-    public function testShouldDetectIfADirectiveArgumentWasRemoved()
+    public function testShouldDetectIfADirectiveArgumentWasRemoved() : void
     {
         $oldSchema = new Schema([
             'directives' => [
@@ -1332,7 +1332,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a non-nullable directive argument was added')
      */
-    public function testShouldDetectIfANonNullableDirectiveArgumentWasAdded()
+    public function testShouldDetectIfANonNullableDirectiveArgumentWasAdded() : void
     {
         $oldSchema = new Schema([
             'directives' => [
@@ -1371,7 +1371,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect locations removed from a directive')
      */
-    public function testShouldDetectLocationsRemovedFromADirective()
+    public function testShouldDetectLocationsRemovedFromADirective() : void
     {
         $d1 = new Directive([
             'name' => 'Directive Name',
@@ -1389,7 +1389,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect locations removed directives within a schema')
      */
-    public function testShouldDetectLocationsRemovedDirectiveWithinASchema()
+    public function testShouldDetectLocationsRemovedDirectiveWithinASchema() : void
     {
         $oldSchema = new Schema([
             'directives' => [
@@ -1428,7 +1428,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if an argument's defaultValue has changed')
      */
-    public function testShouldDetectIfAnArgumentsDefaultValueHasChanged()
+    public function testShouldDetectIfAnArgumentsDefaultValueHasChanged() : void
     {
         $oldType = new ObjectType([
             'name' => 'Type1',
@@ -1486,7 +1486,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a value was added to an enum type')
      */
-    public function testShouldDetectIfAValueWasAddedToAnEnumType()
+    public function testShouldDetectIfAValueWasAddedToAnEnumType() : void
     {
         $oldEnumType = new EnumType([
             'name' => 'EnumType1',
@@ -1530,7 +1530,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect interfaces added to types')
      */
-    public function testShouldDetectInterfacesAddedToTypes()
+    public function testShouldDetectInterfacesAddedToTypes() : void
     {
         $interface1 = new InterfaceType([
             'name' => 'Interface1',
@@ -1579,7 +1579,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a type was added to a union type')
      */
-    public function testShouldDetectIfATypeWasAddedToAUnionType()
+    public function testShouldDetectIfATypeWasAddedToAUnionType() : void
     {
         $type1 = new ObjectType([
             'name' => 'Type1',
@@ -1637,7 +1637,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a nullable field was added to an input')
      */
-    public function testShouldDetectIfANullableFieldWasAddedToAnInput()
+    public function testShouldDetectIfANullableFieldWasAddedToAnInput() : void
     {
         $oldInputType = new InputObjectType([
             'name' => 'InputType1',
@@ -1686,7 +1686,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should find all dangerous changes')
      */
-    public function testShouldFindAllDangerousChanges()
+    public function testShouldFindAllDangerousChanges() : void
     {
         $enumThatGainsAValueOld = new EnumType([
             'name' => 'EnumType1',
@@ -1822,7 +1822,7 @@ class BreakingChangesFinderTest extends TestCase
     /**
      * @see it('should detect if a nullable field argument was added')
      */
-    public function testShouldDetectIfANullableFieldArgumentWasAdded()
+    public function testShouldDetectIfANullableFieldArgumentWasAdded() : void
     {
         $oldType = new ObjectType([
             'name' => 'Type1',
diff --git a/tests/Utils/BuildSchemaTest.php b/tests/Utils/BuildSchemaTest.php
index 34b905b..eb0e619 100644
--- a/tests/Utils/BuildSchemaTest.php
+++ b/tests/Utils/BuildSchemaTest.php
@@ -29,7 +29,7 @@ class BuildSchemaTest extends TestCase
     /**
      * @see it('can use built schema for limited execution')
      */
-    public function testUseBuiltSchemaForLimitedExecution()
+    public function testUseBuiltSchemaForLimitedExecution() : void
     {
         $schema = BuildSchema::buildAST(Parser::parse('
             type Query {
@@ -44,7 +44,7 @@ class BuildSchemaTest extends TestCase
     /**
      * @see it('can build a schema directly from the source')
      */
-    public function testBuildSchemaDirectlyFromSource()
+    public function testBuildSchemaDirectlyFromSource() : void
     {
         $schema = BuildSchema::build("
             type Query {
@@ -69,7 +69,7 @@ class BuildSchemaTest extends TestCase
     /**
      * @see it('Simple Type')
      */
-    public function testSimpleType()
+    public function testSimpleType() : void
     {
         $body = '
 type HelloScalars {
@@ -87,7 +87,7 @@ type HelloScalars {
     /**
      * @see it('With directives')
      */
-    public function testWithDirectives()
+    public function testWithDirectives() : void
     {
         $body = '
 directive @foo(arg: Int) on FIELD
@@ -103,7 +103,7 @@ type Query {
     /**
      * @see it('Supports descriptions')
      */
-    public function testSupportsDescriptions()
+    public function testSupportsDescriptions() : void
     {
       $body = '
 """This is a directive"""
@@ -135,7 +135,7 @@ type Query {
     /**
      * @see it('Supports option for comment descriptions')
      */
-    public function testSupportsOptionForCommentDescriptions()
+    public function testSupportsOptionForCommentDescriptions() : void
     {
         $body = '
 # This is a directive
@@ -166,7 +166,7 @@ type Query {
     /**
      * @see it('Maintains @skip & @include')
      */
-    public function testMaintainsSkipAndInclude()
+    public function testMaintainsSkipAndInclude() : void
     {
         $body = '
 type Query {
@@ -183,7 +183,7 @@ type Query {
     /**
      * @see it('Overriding directives excludes specified')
      */
-    public function testOverridingDirectivesExcludesSpecified()
+    public function testOverridingDirectivesExcludesSpecified() : void
     {
         $body = '
 directive @skip on FIELD
@@ -204,7 +204,7 @@ type Query {
     /**
      * @see it('Adding directives maintains @skip & @include')
      */
-    public function testAddingDirectivesMaintainsSkipAndInclude()
+    public function testAddingDirectivesMaintainsSkipAndInclude() : void
     {
         $body = '
       directive @foo(arg: Int) on FIELD
@@ -223,7 +223,7 @@ type Query {
     /**
      * @see it('Type modifiers')
      */
-    public function testTypeModifiers()
+    public function testTypeModifiers() : void
     {
         $body = '
 type HelloScalars {
@@ -241,7 +241,7 @@ type HelloScalars {
     /**
      * @see it('Recursive type')
      */
-    public function testRecursiveType()
+    public function testRecursiveType() : void
     {
         $body = '
 type Query {
@@ -256,7 +256,7 @@ type Query {
     /**
      * @see it('Two types circular')
      */
-    public function testTwoTypesCircular()
+    public function testTwoTypesCircular() : void
     {
         $body = '
 schema {
@@ -280,7 +280,7 @@ type TypeTwo {
     /**
      * @see it('Single argument field')
      */
-    public function testSingleArgumentField()
+    public function testSingleArgumentField() : void
     {
         $body = '
 type Query {
@@ -298,7 +298,7 @@ type Query {
     /**
      * @see it('Simple type with multiple arguments')
      */
-    public function testSimpleTypeWithMultipleArguments()
+    public function testSimpleTypeWithMultipleArguments() : void
     {
         $body = '
 type Query {
@@ -312,7 +312,7 @@ type Query {
     /**
      * @see it('Simple type with interface')
      */
-    public function testSimpleTypeWithInterface()
+    public function testSimpleTypeWithInterface() : void
     {
         $body = '
 type Query implements WorldInterface {
@@ -330,7 +330,7 @@ interface WorldInterface {
     /**
      * @see it('Simple output enum')
      */
-    public function testSimpleOutputEnum()
+    public function testSimpleOutputEnum() : void
     {
         $body = '
 enum Hello {
@@ -348,7 +348,7 @@ type Query {
     /**
      * @see it('Simple input enum')
      */
-    public function testSimpleInputEnum()
+    public function testSimpleInputEnum() : void
     {
         $body = '
 enum Hello {
@@ -366,7 +366,7 @@ type Query {
     /**
      * @see it('Multiple value enum')
      */
-    public function testMultipleValueEnum()
+    public function testMultipleValueEnum() : void
     {
         $body = '
 enum Hello {
@@ -385,7 +385,7 @@ type Query {
     /**
      * @see it('Simple Union')
      */
-    public function testSimpleUnion()
+    public function testSimpleUnion() : void
     {
         $body = '
 union Hello = World
@@ -405,7 +405,7 @@ type World {
     /**
      * @see it('Multiple Union')
      */
-    public function testMultipleUnion()
+    public function testMultipleUnion() : void
     {
         $body = '
 union Hello = WorldOne | WorldTwo
@@ -429,7 +429,7 @@ type WorldTwo {
     /**
      * @see it('Specifying Union type using __typename')
      */
-    public function testSpecifyingUnionTypeUsingTypename()
+    public function testSpecifyingUnionTypeUsingTypename() : void
     {
         $schema = BuildSchema::buildAST(Parser::parse('
             type Query {
@@ -486,7 +486,7 @@ type WorldTwo {
     /**
      * @see it('Specifying Interface type using __typename')
      */
-    public function testSpecifyingInterfaceUsingTypename()
+    public function testSpecifyingInterfaceUsingTypename() : void
     {
         $schema = BuildSchema::buildAST(Parser::parse('
             type Query {
@@ -550,7 +550,7 @@ type WorldTwo {
     /**
      * @see it('Custom Scalar')
      */
-    public function testCustomScalar()
+    public function testCustomScalar() : void
     {
         $body = '
 scalar CustomScalar
@@ -566,7 +566,7 @@ type Query {
     /**
      * @see it('Input Object')
      */
-    public function testInputObject()
+    public function testInputObject() : void
     {
         $body = '
 input Input {
@@ -584,7 +584,7 @@ type Query {
     /**
      * @see it('Simple argument field with default')
      */
-    public function testSimpleArgumentFieldWithDefault()
+    public function testSimpleArgumentFieldWithDefault() : void
     {
         $body = '
 type Query {
@@ -598,7 +598,7 @@ type Query {
     /**
      * @see it('Custom scalar argument field with default')
      */
-    public function testCustomScalarArgumentFieldWithDefault()
+    public function testCustomScalarArgumentFieldWithDefault() : void
     {
         $body = '
 scalar CustomScalar
@@ -614,7 +614,7 @@ type Query {
     /**
      * @see it('Simple type with mutation')
      */
-    public function testSimpleTypeWithMutation()
+    public function testSimpleTypeWithMutation() : void
     {
         $body = '
 schema {
@@ -639,7 +639,7 @@ type Mutation {
     /**
      * @see it('Simple type with subscription')
      */
-    public function testSimpleTypeWithSubscription()
+    public function testSimpleTypeWithSubscription() : void
     {
         $body = '
 schema {
@@ -664,7 +664,7 @@ type Subscription {
     /**
      * @see it('Unreferenced type implementing referenced interface')
      */
-    public function testUnreferencedTypeImplementingReferencedInterface()
+    public function testUnreferencedTypeImplementingReferencedInterface() : void
     {
         $body = '
 type Concrete implements Iface {
@@ -686,7 +686,7 @@ type Query {
     /**
      * @see it('Unreferenced type implementing referenced union')
      */
-    public function testUnreferencedTypeImplementingReferencedUnion()
+    public function testUnreferencedTypeImplementingReferencedUnion() : void
     {
         $body = '
 type Concrete {
@@ -706,7 +706,7 @@ union Union = Concrete
     /**
      * @see it('Supports @deprecated')
      */
-    public function testSupportsDeprecated()
+    public function testSupportsDeprecated() : void
     {
         $body = '
 enum MyEnum {
@@ -752,7 +752,7 @@ type Query {
     /**
      * @see it('Correctly assign AST nodes')
      */
-    public function testCorrectlyAssignASTNodes()
+    public function testCorrectlyAssignASTNodes() : void
     {
         $schemaAST = Parser::parse('
       schema {
@@ -823,7 +823,7 @@ type Query {
     /**
      * @see it('Root operation types with custom names')
      */
-    public function testRootOperationTypesWithCustomNames()
+    public function testRootOperationTypesWithCustomNames() : void
     {
         $schema = BuildSchema::build('
           schema {
@@ -844,7 +844,7 @@ type Query {
     /**
      * @see it('Default root operation type names')
      */
-    public function testDefaultRootOperationTypeNames()
+    public function testDefaultRootOperationTypeNames() : void
     {
         $schema = BuildSchema::build('
           type Query { str: String }
@@ -859,7 +859,7 @@ type Query {
     /**
      * @see it('can build invalid schema')
      */
-    public function testCanBuildInvalidSchema()
+    public function testCanBuildInvalidSchema() : void
     {
         $schema = BuildSchema::build('
           # Invalid schema, because it is missing query root type
@@ -876,7 +876,7 @@ type Query {
     /**
      * @see it('Allows only a single schema definition')
      */
-    public function testAllowsOnlySingleSchemaDefinition()
+    public function testAllowsOnlySingleSchemaDefinition() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Must provide only one schema definition.');
@@ -900,7 +900,7 @@ type Hello {
     /**
      * @see it('Allows only a single query type')
      */
-    public function testAllowsOnlySingleQueryType()
+    public function testAllowsOnlySingleQueryType() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Must provide only one query type in schema.');
@@ -925,7 +925,7 @@ type Yellow {
     /**
      * @see it('Allows only a single mutation type')
      */
-    public function testAllowsOnlySingleMutationType()
+    public function testAllowsOnlySingleMutationType() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Must provide only one mutation type in schema.');
@@ -951,7 +951,7 @@ type Yellow {
     /**
      * @see it('Allows only a single subscription type')
      */
-    public function testAllowsOnlySingleSubscriptionType()
+    public function testAllowsOnlySingleSubscriptionType() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Must provide only one subscription type in schema.');
@@ -977,7 +977,7 @@ type Yellow {
     /**
      * @see it('Unknown type referenced')
      */
-    public function testUnknownTypeReferenced()
+    public function testUnknownTypeReferenced() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Type "Bar" not found in document.');
@@ -998,7 +998,7 @@ type Hello {
     /**
      * @see it('Unknown type in interface list')
      */
-    public function testUnknownTypeInInterfaceList()
+    public function testUnknownTypeInInterfaceList() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Type "Bar" not found in document.');
@@ -1015,7 +1015,7 @@ type Query implements Bar {
     /**
      * @see it('Unknown type in union list')
      */
-    public function testUnknownTypeInUnionList()
+    public function testUnknownTypeInUnionList() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Type "Bar" not found in document.');
@@ -1031,7 +1031,7 @@ type Query { testUnion: TestUnion }
     /**
      * @see it('Unknown query type')
      */
-    public function testUnknownQueryType()
+    public function testUnknownQueryType() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Specified query type "Wat" not found in document.');
@@ -1051,7 +1051,7 @@ type Hello {
     /**
      * @see it('Unknown mutation type')
      */
-    public function testUnknownMutationType()
+    public function testUnknownMutationType() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Specified mutation type "Wat" not found in document.');
@@ -1072,7 +1072,7 @@ type Hello {
     /**
      * @see it('Unknown subscription type')
      */
-    public function testUnknownSubscriptionType()
+    public function testUnknownSubscriptionType() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Specified subscription type "Awesome" not found in document.');
@@ -1098,7 +1098,7 @@ type Wat {
     /**
      * @see it('Does not consider operation names')
      */
-    public function testDoesNotConsiderOperationNames()
+    public function testDoesNotConsiderOperationNames() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Specified query type "Foo" not found in document.');
@@ -1116,7 +1116,7 @@ query Foo { field }
     /**
      * @see it('Does not consider fragment names')
      */
-    public function testDoesNotConsiderFragmentNames()
+    public function testDoesNotConsiderFragmentNames() : void
     {
         $this->expectException(Error::class);
         $this->expectExceptionMessage('Specified query type "Foo" not found in document.');
@@ -1134,7 +1134,7 @@ fragment Foo on Type { field }
     /**
      * @see it('Forbids duplicate type definitions')
      */
-    public function testForbidsDuplicateTypeDefinitions()
+    public function testForbidsDuplicateTypeDefinitions() : void
     {
         $body = '
 schema {
@@ -1156,7 +1156,7 @@ type Repeated {
         BuildSchema::buildAST($doc);
     }
 
-    public function testSupportsTypeConfigDecorator()
+    public function testSupportsTypeConfigDecorator() : void
     {
         $body = '
 schema {
@@ -1231,7 +1231,7 @@ interface Hello {
         $this->assertEquals('My description of Hello', $schema->getType('Hello')->description);
     }
 
-    public function testCreatesTypesLazily()
+    public function testCreatesTypesLazily() : void
     {
         $body = '
 schema {
diff --git a/tests/Utils/CoerceValueTest.php b/tests/Utils/CoerceValueTest.php
index 6ff0e38..0585214 100644
--- a/tests/Utils/CoerceValueTest.php
+++ b/tests/Utils/CoerceValueTest.php
@@ -39,7 +39,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('coercing an array to GraphQLString produces an error')
      */
-    public function testCoercingAnArrayToGraphQLStringProducesAnError()
+    public function testCoercingAnArrayToGraphQLStringProducesAnError() : void
     {
         $result = Value::coerceValue([1, 2, 3], Type::string());
         $this->expectError(
@@ -58,7 +58,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for int input')
      */
-    public function testIntReturnsNoErrorForIntInput()
+    public function testIntReturnsNoErrorForIntInput() : void
     {
         $result = Value::coerceValue('1', Type::int());
         $this->expectNoErrors($result);
@@ -67,7 +67,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for negative int input')
      */
-    public function testIntReturnsNoErrorForNegativeIntInput()
+    public function testIntReturnsNoErrorForNegativeIntInput() : void
     {
         $result = Value::coerceValue('-1', Type::int());
         $this->expectNoErrors($result);
@@ -76,7 +76,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for exponent input')
      */
-    public function testIntReturnsNoErrorForExponentInput()
+    public function testIntReturnsNoErrorForExponentInput() : void
     {
         $result = Value::coerceValue('1e3', Type::int());
         $this->expectNoErrors($result);
@@ -85,7 +85,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for null')
      */
-    public function testIntReturnsASingleErrorNull()
+    public function testIntReturnsASingleErrorNull() : void
     {
         $result = Value::coerceValue(null, Type::int());
         $this->expectNoErrors($result);
@@ -94,7 +94,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns a single error for empty value')
      */
-    public function testIntReturnsASingleErrorForEmptyValue()
+    public function testIntReturnsASingleErrorForEmptyValue() : void
     {
         $result = Value::coerceValue('', Type::int());
         $this->expectError(
@@ -106,7 +106,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns error for float input as int')
      */
-    public function testIntReturnsErrorForFloatInputAsInt()
+    public function testIntReturnsErrorForFloatInputAsInt() : void
     {
         $result = Value::coerceValue('1.5', Type::int());
         $this->expectError(
@@ -118,7 +118,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns a single error for char input')
      */
-    public function testIntReturnsASingleErrorForCharInput()
+    public function testIntReturnsASingleErrorForCharInput() : void
     {
         $result = Value::coerceValue('a', Type::int());
         $this->expectError(
@@ -130,7 +130,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns a single error for multi char input')
      */
-    public function testIntReturnsASingleErrorForMultiCharInput()
+    public function testIntReturnsASingleErrorForMultiCharInput() : void
     {
         $result = Value::coerceValue('meow', Type::int());
         $this->expectError(
@@ -144,7 +144,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for int input')
      */
-    public function testFloatReturnsNoErrorForIntInput()
+    public function testFloatReturnsNoErrorForIntInput() : void
     {
         $result = Value::coerceValue('1', Type::float());
         $this->expectNoErrors($result);
@@ -153,7 +153,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for exponent input')
      */
-    public function testFloatReturnsNoErrorForExponentInput()
+    public function testFloatReturnsNoErrorForExponentInput() : void
     {
         $result = Value::coerceValue('1e3', Type::float());
         $this->expectNoErrors($result);
@@ -162,7 +162,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for float input')
      */
-    public function testFloatReturnsNoErrorForFloatInput()
+    public function testFloatReturnsNoErrorForFloatInput() : void
     {
         $result = Value::coerceValue('1.5', Type::float());
         $this->expectNoErrors($result);
@@ -171,7 +171,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for null')
      */
-    public function testFloatReturnsASingleErrorNull()
+    public function testFloatReturnsASingleErrorNull() : void
     {
         $result = Value::coerceValue(null, Type::float());
         $this->expectNoErrors($result);
@@ -180,7 +180,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns a single error for empty value')
      */
-    public function testFloatReturnsASingleErrorForEmptyValue()
+    public function testFloatReturnsASingleErrorForEmptyValue() : void
     {
         $result = Value::coerceValue('', Type::float());
         $this->expectError(
@@ -192,7 +192,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns a single error for char input')
      */
-    public function testFloatReturnsASingleErrorForCharInput()
+    public function testFloatReturnsASingleErrorForCharInput() : void
     {
         $result = Value::coerceValue('a', Type::float());
         $this->expectError(
@@ -204,7 +204,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns a single error for multi char input')
      */
-    public function testFloatReturnsASingleErrorForMultiCharInput()
+    public function testFloatReturnsASingleErrorForMultiCharInput() : void
     {
         $result = Value::coerceValue('meow', Type::float());
         $this->expectError(
@@ -218,7 +218,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for a known enum name')
      */
-    public function testReturnsNoErrorForAKnownEnumName()
+    public function testReturnsNoErrorForAKnownEnumName() : void
     {
         $fooResult = Value::coerceValue('FOO', $this->testEnum);
         $this->expectNoErrors($fooResult);
@@ -232,7 +232,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('results error for misspelled enum value')
      */
-    public function testReturnsErrorForMisspelledEnumValue()
+    public function testReturnsErrorForMisspelledEnumValue() : void
     {
         $result = Value::coerceValue('foo', $this->testEnum);
         $this->expectError($result, 'Expected type TestEnum; did you mean FOO?');
@@ -241,7 +241,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('results error for incorrect value type')
      */
-    public function testReturnsErrorForIncorrectValueType()
+    public function testReturnsErrorForIncorrectValueType() : void
     {
         $result1 = Value::coerceValue(123, $this->testEnum);
         $this->expectError($result1, 'Expected type TestEnum.');
@@ -255,7 +255,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for a valid input')
      */
-    public function testReturnsNoErrorForValidInput()
+    public function testReturnsNoErrorForValidInput() : void
     {
         $result = Value::coerceValue(['foo' => 123], $this->testInputObject);
         $this->expectNoErrors($result);
@@ -265,7 +265,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for a non-object type')
      */
-    public function testReturnsErrorForNonObjectType()
+    public function testReturnsErrorForNonObjectType() : void
     {
         $result = Value::coerceValue(123, $this->testInputObject);
         $this->expectError($result, 'Expected type TestInputObject to be an object.');
@@ -274,7 +274,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns no error for an invalid field')
      */
-    public function testReturnErrorForAnInvalidField()
+    public function testReturnErrorForAnInvalidField() : void
     {
         $result = Value::coerceValue(['foo' => 'abc'], $this->testInputObject);
         $this->expectError($result, 'Expected type Int at value.foo; Int cannot represent non 32-bit signed integer value: abc');
@@ -283,7 +283,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns multiple errors for multiple invalid fields')
      */
-    public function testReturnsMultipleErrorsForMultipleInvalidFields()
+    public function testReturnsMultipleErrorsForMultipleInvalidFields() : void
     {
         $result = Value::coerceValue(['foo' => 'abc', 'bar' => 'def'], $this->testInputObject);
         $this->assertEquals([
@@ -295,7 +295,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns error for a missing required field')
      */
-    public function testReturnsErrorForAMissingRequiredField()
+    public function testReturnsErrorForAMissingRequiredField() : void
     {
         $result = Value::coerceValue(['bar' => 123], $this->testInputObject);
         $this->expectError($result, 'Field value.foo of required type Int! was not provided.');
@@ -304,7 +304,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns error for an unknown field')
      */
-    public function testReturnsErrorForAnUnknownField()
+    public function testReturnsErrorForAnUnknownField() : void
     {
         $result = Value::coerceValue(['foo' => 123, 'unknownField' => 123], $this->testInputObject);
         $this->expectError($result, 'Field "unknownField" is not defined by type TestInputObject.');
@@ -313,7 +313,7 @@ class CoerceValueTest extends TestCase
     /**
      * @see it('returns error for a misspelled field')
      */
-    public function testReturnsErrorForAMisspelledField()
+    public function testReturnsErrorForAMisspelledField() : void
     {
         $result = Value::coerceValue(['foo' => 123, 'bart' => 123], $this->testInputObject);
         $this->expectError($result, 'Field "bart" is not defined by type TestInputObject; did you mean bar?');
diff --git a/tests/Utils/ExtractTypesTest.php b/tests/Utils/ExtractTypesTest.php
index 5e2b093..8818899 100644
--- a/tests/Utils/ExtractTypesTest.php
+++ b/tests/Utils/ExtractTypesTest.php
@@ -274,7 +274,7 @@ class ExtractTypesTest extends TestCase
         ]);
     }
 
-    public function testExtractTypesFromQuery()
+    public function testExtractTypesFromQuery() : void
     {
         $expectedTypeMap = [
             'Query' => $this->query,
@@ -291,7 +291,7 @@ class ExtractTypesTest extends TestCase
         $this->assertEquals($expectedTypeMap, $actualTypeMap);
     }
 
-    public function testExtractTypesFromMutation()
+    public function testExtractTypesFromMutation() : void
     {
         $expectedTypeMap = [
             'Mutation' => $this->mutation,
@@ -313,7 +313,7 @@ class ExtractTypesTest extends TestCase
         $this->assertEquals($expectedTypeMap, $actualTypeMap);
     }
 
-    public function testThrowsOnMultipleTypesWithSameName()
+    public function testThrowsOnMultipleTypesWithSameName() : void
     {
         $otherUserType = new ObjectType([
             'name' => 'User',
diff --git a/tests/Utils/IsValidLiteralValueTest.php b/tests/Utils/IsValidLiteralValueTest.php
index 6ad69b9..9f322e4 100644
--- a/tests/Utils/IsValidLiteralValueTest.php
+++ b/tests/Utils/IsValidLiteralValueTest.php
@@ -15,7 +15,7 @@ class IsValidLiteralValueTest extends TestCase
     /**
      * @see it('Returns no errors for a valid value')
      */
-    public function testReturnsNoErrorsForAValidValue()
+    public function testReturnsNoErrorsForAValidValue() : void
     {
         $this->assertEquals(
             [],
@@ -26,7 +26,7 @@ class IsValidLiteralValueTest extends TestCase
     /**
      * @see it('Returns errors for an invalid value')
      */
-    public function testReturnsErrorsForForInvalidValue()
+    public function testReturnsErrorsForForInvalidValue() : void
     {
         $errors = DocumentValidator::isValidLiteralValue(Type::int(), Parser::parseValue('"abc"'));
 
diff --git a/tests/Utils/MixedStoreTest.php b/tests/Utils/MixedStoreTest.php
index a5d0054..2addef3 100644
--- a/tests/Utils/MixedStoreTest.php
+++ b/tests/Utils/MixedStoreTest.php
@@ -35,14 +35,14 @@ class MixedStoreTest extends TestCase
         ];
     }
 
-    public function testAcceptsNullKeys()
+    public function testAcceptsNullKeys() : void
     {
         foreach ($this->getPossibleValues() as $value) {
             $this->assertAcceptsKeyValue(null, $value);
         }
     }
 
-    public function testAcceptsBoolKeys()
+    public function testAcceptsBoolKeys() : void
     {
         foreach ($this->getPossibleValues() as $value) {
             $this->assertAcceptsKeyValue(false, $value);
@@ -52,7 +52,7 @@ class MixedStoreTest extends TestCase
         }
     }
 
-    public function testAcceptsIntKeys()
+    public function testAcceptsIntKeys() : void
     {
         foreach ($this->getPossibleValues() as $value) {
             $this->assertAcceptsKeyValue(-100000, $value);
@@ -63,7 +63,7 @@ class MixedStoreTest extends TestCase
         }
     }
 
-    public function testAcceptsFloatKeys()
+    public function testAcceptsFloatKeys() : void
     {
         foreach ($this->getPossibleValues() as $value) {
             $this->assertAcceptsKeyValue(-100000.5, $value);
@@ -76,7 +76,7 @@ class MixedStoreTest extends TestCase
         }
     }
 
-    public function testAcceptsArrayKeys()
+    public function testAcceptsArrayKeys() : void
     {
         foreach ($this->getPossibleValues() as $value) {
             $this->assertAcceptsKeyValue([], $value);
@@ -88,7 +88,7 @@ class MixedStoreTest extends TestCase
         }
     }
 
-    public function testAcceptsObjectKeys()
+    public function testAcceptsObjectKeys() : void
     {
         foreach ($this->getPossibleValues() as $value) {
             $this->assertAcceptsKeyValue(new \stdClass(), $value);
diff --git a/tests/Utils/QuotedOrListTest.php b/tests/Utils/QuotedOrListTest.php
index 6937ad7..4b0c7b1 100644
--- a/tests/Utils/QuotedOrListTest.php
+++ b/tests/Utils/QuotedOrListTest.php
@@ -14,7 +14,7 @@ class QuotedOrListTest extends TestCase
     /**
      * @see it('Does not accept an empty list')
      */
-    public function testResturnsResultsWhenInputIsEmpty()
+    public function testResturnsResultsWhenInputIsEmpty() : void
     {
         $this->expectException(\LogicException::class);
         Utils::quotedOrList([]);
@@ -23,7 +23,7 @@ class QuotedOrListTest extends TestCase
     /**
      * @see it('Returns single quoted item')
      */
-    public function testReturnsSingleQuotedItem()
+    public function testReturnsSingleQuotedItem() : void
     {
         $this->assertEquals(
             '"A"',
@@ -34,7 +34,7 @@ class QuotedOrListTest extends TestCase
     /**
      * @see it('Returns two item list')
      */
-    public function testReturnsTwoItemList()
+    public function testReturnsTwoItemList() : void
     {
         $this->assertEquals(
             '"A" or "B"',
@@ -45,7 +45,7 @@ class QuotedOrListTest extends TestCase
     /**
      * @see it('Returns comma separated many item list')
      */
-    public function testReturnsCommaSeparatedManyItemList()
+    public function testReturnsCommaSeparatedManyItemList() : void
     {
         $this->assertEquals(
             '"A", "B", or "C"',
@@ -56,7 +56,7 @@ class QuotedOrListTest extends TestCase
     /**
      * @see it('Limits to five items')
      */
-    public function testLimitsToFiveItems()
+    public function testLimitsToFiveItems() : void
     {
         $this->assertEquals(
             '"A", "B", "C", "D", or "E"',
diff --git a/tests/Utils/SchemaPrinterTest.php b/tests/Utils/SchemaPrinterTest.php
index cfd6f51..90caae5 100644
--- a/tests/Utils/SchemaPrinterTest.php
+++ b/tests/Utils/SchemaPrinterTest.php
@@ -40,7 +40,7 @@ class SchemaPrinterTest extends TestCase
     /**
      * @see it('Prints String Field')
      */
-    public function testPrintsStringField()
+    public function testPrintsStringField() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string()
@@ -55,7 +55,7 @@ type Query {
     /**
      * @see it('Prints [String] Field')
      */
-    public function testPrintArrayStringField()
+    public function testPrintArrayStringField() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::listOf(Type::string())
@@ -70,7 +70,7 @@ type Query {
     /**
      * @see it('Prints String! Field')
      */
-    public function testPrintNonNullStringField()
+    public function testPrintNonNullStringField() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::nonNull(Type::string())
@@ -85,7 +85,7 @@ type Query {
     /**
      * @see it('Prints [String]! Field')
      */
-    public function testPrintNonNullArrayStringField()
+    public function testPrintNonNullArrayStringField() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::nonNull(Type::listOf(Type::string()))
@@ -100,7 +100,7 @@ type Query {
     /**
      * @see it('Prints [String!] Field')
      */
-    public function testPrintArrayNonNullStringField()
+    public function testPrintArrayNonNullStringField() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::listOf(Type::nonNull(Type::string()))
@@ -115,7 +115,7 @@ type Query {
     /**
      * @see it('Prints [String!]! Field')
      */
-    public function testPrintNonNullArrayNonNullStringField()
+    public function testPrintNonNullArrayNonNullStringField() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::nonNull(Type::listOf(Type::nonNull(Type::string())))
@@ -130,7 +130,7 @@ type Query {
     /**
      * @see it('Print Object Field')
      */
-    public function testPrintObjectField()
+    public function testPrintObjectField() : void
     {
         $fooType = new ObjectType([
             'name' => 'Foo',
@@ -158,7 +158,7 @@ type Query {
     /**
      * @see it('Prints String Field With Int Arg')
      */
-    public function testPrintsStringFieldWithIntArg()
+    public function testPrintsStringFieldWithIntArg() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string(),
@@ -174,7 +174,7 @@ type Query {
     /**
      * @see it('Prints String Field With Int Arg With Default')
      */
-    public function testPrintsStringFieldWithIntArgWithDefault()
+    public function testPrintsStringFieldWithIntArgWithDefault() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string(),
@@ -190,7 +190,7 @@ type Query {
     /**
      * @see it('Prints String Field With String Arg With Default')
      */
-    public function testPrintsStringFieldWithStringArgWithDefault()
+    public function testPrintsStringFieldWithStringArgWithDefault() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string(),
@@ -206,7 +206,7 @@ type Query {
     /**
      * @see it('Prints String Field With Int Arg With Default Null')
      */
-    public function testPrintsStringFieldWithIntArgWithDefaultNull()
+    public function testPrintsStringFieldWithIntArgWithDefaultNull() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string(),
@@ -222,7 +222,7 @@ type Query {
     /**
      * @see it('Prints String Field With Int! Arg')
      */
-    public function testPrintsStringFieldWithNonNullIntArg()
+    public function testPrintsStringFieldWithNonNullIntArg() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string(),
@@ -238,7 +238,7 @@ type Query {
     /**
      * @see it('Prints String Field With Multiple Args')
      */
-    public function testPrintsStringFieldWithMultipleArgs()
+    public function testPrintsStringFieldWithMultipleArgs() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string(),
@@ -257,7 +257,7 @@ type Query {
     /**
      * @see it('Prints String Field With Multiple Args, First is Default')
      */
-    public function testPrintsStringFieldWithMultipleArgsFirstIsDefault()
+    public function testPrintsStringFieldWithMultipleArgsFirstIsDefault() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string(),
@@ -277,7 +277,7 @@ type Query {
     /**
      * @see it('Prints String Field With Multiple Args, Second is Default')
      */
-    public function testPrintsStringFieldWithMultipleArgsSecondIsDefault()
+    public function testPrintsStringFieldWithMultipleArgsSecondIsDefault() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string(),
@@ -297,7 +297,7 @@ type Query {
     /**
      * @see it('Prints String Field With Multiple Args, Last is Default')
      */
-    public function testPrintsStringFieldWithMultipleArgsLastIsDefault()
+    public function testPrintsStringFieldWithMultipleArgsLastIsDefault() : void
     {
         $output = $this->printSingleFieldSchema([
             'type' => Type::string(),
@@ -317,7 +317,7 @@ type Query {
     /**
      * @see it('Prints custom query root type')
      */
-    public function testPrintsCustomQueryRootType()
+    public function testPrintsCustomQueryRootType() : void
     {
         $customQueryType = new ObjectType([
             'name' => 'CustomQueryType',
@@ -343,7 +343,7 @@ type CustomQueryType {
     /**
      * @see it('Print Interface')
      */
-    public function testPrintInterface()
+    public function testPrintInterface() : void
     {
         $fooType = new InterfaceType([
             'name' => 'Foo',
@@ -384,7 +384,7 @@ type Query {
     /**
      * @see it('Print Multiple Interface')
      */
-    public function testPrintMultipleInterface()
+    public function testPrintMultipleInterface() : void
     {
         $fooType = new InterfaceType([
             'name' => 'Foo',
@@ -438,7 +438,7 @@ type Query {
     /**
      * @see it('Print Unions')
      */
-    public function testPrintUnions()
+    public function testPrintUnions() : void
     {
         $fooType = new ObjectType([
             'name' => 'Foo',
@@ -493,7 +493,7 @@ union SingleUnion = Foo
     /**
      * @see it('Print Input Type')
      */
-    public function testInputType()
+    public function testInputType() : void
     {
         $inputType = new InputObjectType([
             'name' => 'InputType',
@@ -526,7 +526,7 @@ type Query {
     /**
      * @see it('Custom Scalar')
      */
-    public function testCustomScalar()
+    public function testCustomScalar() : void
     {
         $oddType = new CustomScalarType([
             'name' => 'Odd',
@@ -556,7 +556,7 @@ type Query {
     /**
      * @see it('Enum')
      */
-    public function testEnum()
+    public function testEnum() : void
     {
         $RGBType = new EnumType([
             'name' => 'RGB',
@@ -592,7 +592,7 @@ enum RGB {
     /**
      * @see it('Prints custom directives')
      */
-    public function testPrintsCustomDirectives()
+    public function testPrintsCustomDirectives() : void
     {
         $query = new ObjectType([
             'name' => 'Query',
@@ -626,7 +626,7 @@ type Query {
     /**
      * @see it('One-line prints a short description')
      */
-    public function testOneLinePrintsAShortDescription()
+    public function testOneLinePrintsAShortDescription() : void
     {
         $description = 'This field is awesome';
         $output = $this->printSingleFieldSchema([
@@ -649,7 +649,7 @@ type Query {
     /**
      * @see it('Does not one-line print a description that ends with a quote')
      */
-    public function testDoesNotOneLinePrintADescriptionThatEndsWithAQuote()
+    public function testDoesNotOneLinePrintADescriptionThatEndsWithAQuote() : void
     {
         $description = 'This field is "awesome"';
         $output = $this->printSingleFieldSchema([
@@ -674,7 +674,7 @@ type Query {
     /**
      * @see it('Preserves leading spaces when printing a description')
      */
-    public function testPReservesLeadingSpacesWhenPrintingADescription()
+    public function testPReservesLeadingSpacesWhenPrintingADescription() : void
     {
         $description = '    This field is "awesome"';
         $output = $this->printSingleFieldSchema([
@@ -698,7 +698,7 @@ type Query {
     /**
      * @see it('Print Introspection Schema')
      */
-    public function testPrintIntrospectionSchema()
+    public function testPrintIntrospectionSchema() : void
     {
         $query = new ObjectType([
             'name' => 'Query',
@@ -943,7 +943,7 @@ EOT;
     /**
      * @see it('Print Introspection Schema with comment descriptions')
      */
-    public function testPrintIntrospectionSchemaWithCommentDescriptions()
+    public function testPrintIntrospectionSchemaWithCommentDescriptions() : void
     {
         $query = new ObjectType([
             'name' => 'Query',
diff --git a/tests/Utils/SuggestionListTest.php b/tests/Utils/SuggestionListTest.php
index 18205e9..dcb152f 100644
--- a/tests/Utils/SuggestionListTest.php
+++ b/tests/Utils/SuggestionListTest.php
@@ -14,7 +14,7 @@ class SuggestionListTest extends TestCase
     /**
      * @see it('Returns results when input is empty')
      */
-    public function testResturnsResultsWhenInputIsEmpty()
+    public function testResturnsResultsWhenInputIsEmpty() : void
     {
         $this->assertEquals(
             Utils::suggestionList('', ['a']),
@@ -25,7 +25,7 @@ class SuggestionListTest extends TestCase
     /**
      * @see it('Returns empty array when there are no options')
      */
-    public function testReturnsEmptyArrayWhenThereAreNoOptions()
+    public function testReturnsEmptyArrayWhenThereAreNoOptions() : void
     {
         $this->assertEquals(
             Utils::suggestionList('input', []),
@@ -36,7 +36,7 @@ class SuggestionListTest extends TestCase
     /**
      * @see it('Returns options sorted based on similarity')
      */
-    public function testReturnsOptionsSortedBasedOnSimilarity()
+    public function testReturnsOptionsSortedBasedOnSimilarity() : void
     {
         $this->assertEquals(
             Utils::suggestionList('abc', ['a', 'ab', 'abc']),
diff --git a/tests/Utils/ValueFromAstTest.php b/tests/Utils/ValueFromAstTest.php
index 3e54576..a9dfca9 100644
--- a/tests/Utils/ValueFromAstTest.php
+++ b/tests/Utils/ValueFromAstTest.php
@@ -25,7 +25,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('rejects empty input')
      */
-    public function testRejectsEmptyInput()
+    public function testRejectsEmptyInput() : void
     {
         $this->assertEquals(Utils::undefined(), AST::valueFromAST(null, Type::boolean()));
     }
@@ -33,7 +33,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('converts according to input coercion rules')
      */
-    public function testConvertsAccordingToInputCoercionRules()
+    public function testConvertsAccordingToInputCoercionRules() : void
     {
         $this->runTestCase(Type::boolean(), 'true', true);
         $this->runTestCase(Type::boolean(), 'false', false);
@@ -48,7 +48,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('does not convert when input coercion rules reject a value')
      */
-    public function testDoesNotConvertWhenInputCoercionRulesRejectAValue()
+    public function testDoesNotConvertWhenInputCoercionRulesRejectAValue() : void
     {
         $undefined = Utils::undefined();
 
@@ -65,7 +65,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('converts enum values according to input coercion rules')
      */
-    public function testConvertsEnumValuesAccordingToInputCoercionRules()
+    public function testConvertsEnumValuesAccordingToInputCoercionRules() : void
     {
         $testEnum = new EnumType([
             'name' => 'TestColor',
@@ -88,7 +88,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('coerces to null unless non-null')
      */
-    public function testCoercesToNullUnlessNonNull()
+    public function testCoercesToNullUnlessNonNull() : void
     {
         $this->runTestCase(Type::boolean(), 'null', null);
         $this->runTestCase(Type::nonNull(Type::boolean()), 'null', Utils::undefined());
@@ -97,7 +97,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('coerces lists of values')
      */
-    public function testCoercesListsOfValues()
+    public function testCoercesListsOfValues() : void
     {
         $listOfBool = Type::listOf(Type::boolean());
         $undefined = Utils::undefined();
@@ -114,7 +114,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('coerces non-null lists of values')
      */
-    public function testCoercesNonNullListsOfValues()
+    public function testCoercesNonNullListsOfValues() : void
     {
         $nonNullListOfBool = Type::nonNull(Type::listOf(Type::boolean()));
         $undefined = Utils::undefined();
@@ -130,7 +130,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('coerces lists of non-null values')
      */
-    public function testCoercesListsOfNonNullValues()
+    public function testCoercesListsOfNonNullValues() : void
     {
         $listOfNonNullBool = Type::listOf(Type::nonNull(Type::boolean()));
         $undefined = Utils::undefined();
@@ -146,7 +146,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('coerces non-null lists of non-null values')
      */
-    public function testCoercesNonNullListsOfNonNullValues()
+    public function testCoercesNonNullListsOfNonNullValues() : void
     {
         $nonNullListOfNonNullBool = Type::nonNull(Type::listOf(Type::nonNull(Type::boolean())));
         $undefined = Utils::undefined();
@@ -176,7 +176,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('coerces input objects according to input coercion rules')
      */
-    public function testCoercesInputObjectsAccordingToInputCoercionRules()
+    public function testCoercesInputObjectsAccordingToInputCoercionRules() : void
     {
         $testInputObj = $this->inputObj();
         $undefined = Utils::undefined();
@@ -194,7 +194,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('accepts variable values assuming already coerced')
      */
-    public function testAcceptsVariableValuesAssumingAlreadyCoerced()
+    public function testAcceptsVariableValuesAssumingAlreadyCoerced() : void
     {
         $this->runTestCaseWithVars([], Type::boolean(), '$var', Utils::undefined());
         $this->runTestCaseWithVars([ 'var' => true ], Type::boolean(), '$var', true);
@@ -204,7 +204,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('asserts variables are provided as items in lists')
      */
-    public function testAssertsVariablesAreProvidedAsItemsInLists()
+    public function testAssertsVariablesAreProvidedAsItemsInLists() : void
     {
         $listOfBool = Type::listOf(Type::boolean());
         $listOfNonNullBool = Type::listOf(Type::nonNull(Type::boolean()));
@@ -221,7 +221,7 @@ class ValueFromAstTest extends TestCase
     /**
      * @see it('omits input object fields for unprovided variables')
      */
-    public function testOmitsInputObjectFieldsForUnprovidedVariables()
+    public function testOmitsInputObjectFieldsForUnprovidedVariables() : void
     {
         $testInputObj = $this->inputObj();
 
diff --git a/tests/UtilsTest.php b/tests/UtilsTest.php
index 84b5e03..facc85b 100644
--- a/tests/UtilsTest.php
+++ b/tests/UtilsTest.php
@@ -6,7 +6,7 @@ use PHPUnit\Framework\TestCase;
 
 class UtilsTest extends TestCase
 {
-    public function testAssignThrowsExceptionOnMissingRequiredKey()
+    public function testAssignThrowsExceptionOnMissingRequiredKey() : void
     {
         $object = new \stdClass();
         $object->requiredKey = 'value';
diff --git a/tests/Validator/DisableIntrospectionTest.php b/tests/Validator/DisableIntrospectionTest.php
index 6bb394d..461daae 100644
--- a/tests/Validator/DisableIntrospectionTest.php
+++ b/tests/Validator/DisableIntrospectionTest.php
@@ -12,7 +12,7 @@ class DisableIntrospectionTest extends ValidatorTestCase
     /**
      * @see it('fails if the query contains __schema')
      */
-    public function testQueryContainsSchema()
+    public function testQueryContainsSchema() : void
     {
         $this->expectFailsRule(new DisableIntrospection(DisableIntrospection::ENABLED), '
       query { 
@@ -30,7 +30,7 @@ class DisableIntrospectionTest extends ValidatorTestCase
     /**
      * @see it('fails if the query contains __type')
      */
-    public function testQueryContainsType()
+    public function testQueryContainsType() : void
     {
         $this->expectFailsRule(new DisableIntrospection(DisableIntrospection::ENABLED), '
       query { 
@@ -48,7 +48,7 @@ class DisableIntrospectionTest extends ValidatorTestCase
     /**
      * @see it('does not fail on a query that does not contain __type')
      */
-    public function testValidQuery()
+    public function testValidQuery() : void
     {
         $this->expectPassesRule(new DisableIntrospection(DisableIntrospection::ENABLED), '
       query {
@@ -66,7 +66,7 @@ class DisableIntrospectionTest extends ValidatorTestCase
     /**
      * @see it('does not fail when not enabled')
      */
-    public function testQueryWhenDisabled()
+    public function testQueryWhenDisabled() : void
     {
         $this->expectPassesRule(new DisableIntrospection(DisableIntrospection::DISABLED), '
       query { 
@@ -82,7 +82,7 @@ class DisableIntrospectionTest extends ValidatorTestCase
     /**
      * @see it('has a public interface for enabeling the rule')
      */
-    public function testPublicEnableInterface()
+    public function testPublicEnableInterface() : void
     {
         $disableIntrospection = new DisableIntrospection(DisableIntrospection::DISABLED);
         $disableIntrospection->setEnabled(DisableIntrospection::ENABLED);
@@ -102,7 +102,7 @@ class DisableIntrospectionTest extends ValidatorTestCase
     /**
      * @see it('has a public interface for disableing the rule')
      */
-    public function testPublicDisableInterface()
+    public function testPublicDisableInterface() : void
     {
         $disableIntrospection = new DisableIntrospection(DisableIntrospection::ENABLED);
         $disableIntrospection->setEnabled(DisableIntrospection::DISABLED);
diff --git a/tests/Validator/ExecutableDefinitionsTest.php b/tests/Validator/ExecutableDefinitionsTest.php
index a12ff2f..28ab13a 100644
--- a/tests/Validator/ExecutableDefinitionsTest.php
+++ b/tests/Validator/ExecutableDefinitionsTest.php
@@ -13,7 +13,7 @@ class ExecutableDefinitionsTest extends ValidatorTestCase
     /**
      * @see it('with only operation')
      */
-    public function testWithOnlyOperation()
+    public function testWithOnlyOperation() : void
     {
         $this->expectPassesRule(new ExecutableDefinitions, '
       query Foo {
@@ -27,7 +27,7 @@ class ExecutableDefinitionsTest extends ValidatorTestCase
     /**
      * @see it('with operation and fragment')
      */
-    public function testWithOperationAndFragment()
+    public function testWithOperationAndFragment() : void
     {
         $this->expectPassesRule(new ExecutableDefinitions, '
       query Foo {
@@ -46,7 +46,7 @@ class ExecutableDefinitionsTest extends ValidatorTestCase
     /**
      * @see it('with typeDefinition')
      */
-    public function testWithTypeDefinition()
+    public function testWithTypeDefinition() : void
     {
         $this->expectFailsRule(new ExecutableDefinitions, '
       query Foo {
diff --git a/tests/Validator/FieldsOnCorrectTypeTest.php b/tests/Validator/FieldsOnCorrectTypeTest.php
index 4f55b1c..a838f3c 100644
--- a/tests/Validator/FieldsOnCorrectTypeTest.php
+++ b/tests/Validator/FieldsOnCorrectTypeTest.php
@@ -12,7 +12,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Object field selection')
      */
-    public function testObjectFieldSelection()
+    public function testObjectFieldSelection() : void
     {
         $this->expectPassesRule(new FieldsOnCorrectType(), '
       fragment objectFieldSelection on Dog {
@@ -25,7 +25,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Aliased object field selection')
      */
-    public function testAliasedObjectFieldSelection()
+    public function testAliasedObjectFieldSelection() : void
     {
         $this->expectPassesRule(new FieldsOnCorrectType, '
       fragment aliasedObjectFieldSelection on Dog {
@@ -38,7 +38,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Interface field selection')
      */
-    public function testInterfaceFieldSelection()
+    public function testInterfaceFieldSelection() : void
     {
         $this->expectPassesRule(new FieldsOnCorrectType, '
       fragment interfaceFieldSelection on Pet {
@@ -51,7 +51,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Aliased interface field selection')
      */
-    public function testAliasedInterfaceFieldSelection()
+    public function testAliasedInterfaceFieldSelection() : void
     {
         $this->expectPassesRule(new FieldsOnCorrectType, '
       fragment interfaceFieldSelection on Pet {
@@ -63,7 +63,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Lying alias selection')
      */
-    public function testLyingAliasSelection()
+    public function testLyingAliasSelection() : void
     {
         $this->expectPassesRule(new FieldsOnCorrectType, '
       fragment lyingAliasSelection on Dog {
@@ -75,7 +75,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Ignores fields on unknown type')
      */
-    public function testIgnoresFieldsOnUnknownType()
+    public function testIgnoresFieldsOnUnknownType() : void
     {
         $this->expectPassesRule(new FieldsOnCorrectType, '
       fragment unknownSelection on UnknownType {
@@ -87,7 +87,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('reports errors when type is known again')
      */
-    public function testReportsErrorsWhenTypeIsKnownAgain()
+    public function testReportsErrorsWhenTypeIsKnownAgain() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment typeKnownAgain on Pet {
@@ -107,7 +107,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Field not defined on fragment')
      */
-    public function testFieldNotDefinedOnFragment()
+    public function testFieldNotDefinedOnFragment() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment fieldNotDefined on Dog {
@@ -120,7 +120,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Ignores deeply unknown field')
      */
-    public function testIgnoresDeeplyUnknownField()
+    public function testIgnoresDeeplyUnknownField() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment deepFieldNotDefined on Dog {
@@ -135,7 +135,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Sub-field not defined')
      */
-    public function testSubFieldNotDefined()
+    public function testSubFieldNotDefined() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment subFieldNotDefined on Human {
@@ -150,7 +150,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Field not defined on inline fragment')
      */
-    public function testFieldNotDefinedOnInlineFragment()
+    public function testFieldNotDefinedOnInlineFragment() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment fieldNotDefined on Pet {
@@ -165,7 +165,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Aliased field target not defined')
      */
-    public function testAliasedFieldTargetNotDefined()
+    public function testAliasedFieldTargetNotDefined() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment aliasedFieldTargetNotDefined on Dog {
@@ -178,7 +178,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Aliased lying field target not defined')
      */
-    public function testAliasedLyingFieldTargetNotDefined()
+    public function testAliasedLyingFieldTargetNotDefined() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment aliasedLyingFieldTargetNotDefined on Dog {
@@ -191,7 +191,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Not defined on interface')
      */
-    public function testNotDefinedOnInterface()
+    public function testNotDefinedOnInterface() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment notDefinedOnInterface on Pet {
@@ -204,7 +204,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Defined on implementors but not on interface')
      */
-    public function testDefinedOnImplmentorsButNotOnInterface()
+    public function testDefinedOnImplmentorsButNotOnInterface() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment definedOnImplementorsButNotInterface on Pet {
@@ -217,7 +217,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Meta field selection on union')
      */
-    public function testMetaFieldSelectionOnUnion()
+    public function testMetaFieldSelectionOnUnion() : void
     {
         $this->expectPassesRule(new FieldsOnCorrectType, '
       fragment directFieldSelectionOnUnion on CatOrDog {
@@ -229,7 +229,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Direct field selection on union')
      */
-    public function testDirectFieldSelectionOnUnion()
+    public function testDirectFieldSelectionOnUnion() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment directFieldSelectionOnUnion on CatOrDog {
@@ -242,7 +242,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Defined on implementors queried on union')
      */
-    public function testDefinedOnImplementorsQueriedOnUnion()
+    public function testDefinedOnImplementorsQueriedOnUnion() : void
     {
         $this->expectFailsRule(new FieldsOnCorrectType, '
       fragment definedOnImplementorsQueriedOnUnion on CatOrDog {
@@ -262,7 +262,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('valid field in inline fragment')
      */
-    public function testValidFieldInInlineFragment()
+    public function testValidFieldInInlineFragment() : void
     {
         $this->expectPassesRule(new FieldsOnCorrectType, '
       fragment objectFieldSelection on Pet {
@@ -278,7 +278,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Works with no suggestions')
      */
-    public function testWorksWithNoSuggestions()
+    public function testWorksWithNoSuggestions() : void
     {
         $this->assertEquals('Cannot query field "f" on type "T".', FieldsOnCorrectType::undefinedFieldMessage('f', 'T', [], []));
     }
@@ -286,7 +286,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Works with no small numbers of type suggestions')
      */
-    public function testWorksWithNoSmallNumbersOfTypeSuggestions()
+    public function testWorksWithNoSmallNumbersOfTypeSuggestions() : void
     {
         $expected = 'Cannot query field "f" on type "T". ' .
             'Did you mean to use an inline fragment on "A" or "B"?';
@@ -297,7 +297,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Works with no small numbers of field suggestions')
      */
-    public function testWorksWithNoSmallNumbersOfFieldSuggestions()
+    public function testWorksWithNoSmallNumbersOfFieldSuggestions() : void
     {
         $expected = 'Cannot query field "f" on type "T". ' .
             'Did you mean "z" or "y"?';
@@ -308,7 +308,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Only shows one set of suggestions at a time, preferring types')
      */
-    public function testOnlyShowsOneSetOfSuggestionsAtATimePreferringTypes()
+    public function testOnlyShowsOneSetOfSuggestionsAtATimePreferringTypes() : void
     {
         $expected = 'Cannot query field "f" on type "T". ' .
             'Did you mean to use an inline fragment on "A" or "B"?';
@@ -319,7 +319,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Limits lots of type suggestions')
      */
-    public function testLimitsLotsOfTypeSuggestions()
+    public function testLimitsLotsOfTypeSuggestions() : void
     {
         $expected = 'Cannot query field "f" on type "T". ' .
             'Did you mean to use an inline fragment on "A", "B", "C", "D", or "E"?';
@@ -335,7 +335,7 @@ class FieldsOnCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Limits lots of field suggestions')
      */
-    public function testLimitsLotsOfFieldSuggestions()
+    public function testLimitsLotsOfFieldSuggestions() : void
     {
         $expected = 'Cannot query field "f" on type "T". ' .
             'Did you mean "z", "y", "x", "w", or "v"?';
diff --git a/tests/Validator/FragmentsOnCompositeTypesTest.php b/tests/Validator/FragmentsOnCompositeTypesTest.php
index c8a0f0a..b1a116a 100644
--- a/tests/Validator/FragmentsOnCompositeTypesTest.php
+++ b/tests/Validator/FragmentsOnCompositeTypesTest.php
@@ -12,7 +12,7 @@ class FragmentsOnCompositeTypesTest extends ValidatorTestCase
     /**
      * @see it('object is valid fragment type')
      */
-    public function testObjectIsValidFragmentType()
+    public function testObjectIsValidFragmentType() : void
     {
         $this->expectPassesRule(new FragmentsOnCompositeTypes, '
       fragment validFragment on Dog {
@@ -24,7 +24,7 @@ class FragmentsOnCompositeTypesTest extends ValidatorTestCase
     /**
      * @see it('interface is valid fragment type')
      */
-    public function testInterfaceIsValidFragmentType()
+    public function testInterfaceIsValidFragmentType() : void
     {
         $this->expectPassesRule(new FragmentsOnCompositeTypes, '
       fragment validFragment on Pet {
@@ -36,7 +36,7 @@ class FragmentsOnCompositeTypesTest extends ValidatorTestCase
     /**
      * @see it('object is valid inline fragment type')
      */
-    public function testObjectIsValidInlineFragmentType()
+    public function testObjectIsValidInlineFragmentType() : void
     {
         $this->expectPassesRule(new FragmentsOnCompositeTypes, '
       fragment validFragment on Pet {
@@ -50,7 +50,7 @@ class FragmentsOnCompositeTypesTest extends ValidatorTestCase
     /**
      * @see it('inline fragment without type is valid')
      */
-    public function testInlineFragmentWithoutTypeIsValid()
+    public function testInlineFragmentWithoutTypeIsValid() : void
     {
         $this->expectPassesRule(new FragmentsOnCompositeTypes, '
       fragment validFragment on Pet {
@@ -64,7 +64,7 @@ class FragmentsOnCompositeTypesTest extends ValidatorTestCase
     /**
      * @see it('union is valid fragment type')
      */
-    public function testUnionIsValidFragmentType()
+    public function testUnionIsValidFragmentType() : void
     {
         $this->expectPassesRule(new FragmentsOnCompositeTypes, '
       fragment validFragment on CatOrDog {
@@ -76,7 +76,7 @@ class FragmentsOnCompositeTypesTest extends ValidatorTestCase
     /**
      * @see it('scalar is invalid fragment type')
      */
-    public function testScalarIsInvalidFragmentType()
+    public function testScalarIsInvalidFragmentType() : void
     {
         $this->expectFailsRule(new FragmentsOnCompositeTypes, '
       fragment scalarFragment on Boolean {
@@ -89,7 +89,7 @@ class FragmentsOnCompositeTypesTest extends ValidatorTestCase
     /**
      * @see it('enum is invalid fragment type')
      */
-    public function testEnumIsInvalidFragmentType()
+    public function testEnumIsInvalidFragmentType() : void
     {
         $this->expectFailsRule(new FragmentsOnCompositeTypes, '
       fragment scalarFragment on FurColor {
@@ -102,7 +102,7 @@ class FragmentsOnCompositeTypesTest extends ValidatorTestCase
     /**
      * @see it('input object is invalid fragment type')
      */
-    public function testInputObjectIsInvalidFragmentType()
+    public function testInputObjectIsInvalidFragmentType() : void
     {
         $this->expectFailsRule(new FragmentsOnCompositeTypes, '
       fragment inputFragment on ComplexInput {
@@ -115,7 +115,7 @@ class FragmentsOnCompositeTypesTest extends ValidatorTestCase
     /**
      * @see it('scalar is invalid inline fragment type')
      */
-    public function testScalarIsInvalidInlineFragmentType()
+    public function testScalarIsInvalidInlineFragmentType() : void
     {
         $this->expectFailsRule(new FragmentsOnCompositeTypes, '
       fragment invalidFragment on Pet {
diff --git a/tests/Validator/KnownArgumentNamesTest.php b/tests/Validator/KnownArgumentNamesTest.php
index eeba12e..8c3fc24 100644
--- a/tests/Validator/KnownArgumentNamesTest.php
+++ b/tests/Validator/KnownArgumentNamesTest.php
@@ -12,7 +12,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('single arg is known')
      */
-    public function testSingleArgIsKnown()
+    public function testSingleArgIsKnown() : void
     {
         $this->expectPassesRule(new KnownArgumentNames, '
       fragment argOnRequiredArg on Dog {
@@ -24,7 +24,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple args are known')
      */
-    public function testMultipleArgsAreKnown()
+    public function testMultipleArgsAreKnown() : void
     {
         $this->expectPassesRule(new KnownArgumentNames, '
       fragment multipleArgs on ComplicatedArgs {
@@ -36,7 +36,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('ignores args of unknown fields')
      */
-    public function testIgnoresArgsOfUnknownFields()
+    public function testIgnoresArgsOfUnknownFields() : void
     {
         $this->expectPassesRule(new KnownArgumentNames, '
       fragment argOnUnknownField on Dog {
@@ -48,7 +48,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple args in reverse order are known')
      */
-    public function testMultipleArgsInReverseOrderAreKnown()
+    public function testMultipleArgsInReverseOrderAreKnown() : void
     {
         $this->expectPassesRule(new KnownArgumentNames, '
       fragment multipleArgsReverseOrder on ComplicatedArgs {
@@ -60,7 +60,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('no args on optional arg')
      */
-    public function testNoArgsOnOptionalArg()
+    public function testNoArgsOnOptionalArg() : void
     {
         $this->expectPassesRule(new KnownArgumentNames, '
       fragment noArgOnOptionalArg on Dog {
@@ -72,7 +72,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('args are known deeply')
      */
-    public function testArgsAreKnownDeeply()
+    public function testArgsAreKnownDeeply() : void
     {
         $this->expectPassesRule(new KnownArgumentNames, '
       {
@@ -93,7 +93,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('directive args are known')
      */
-    public function testDirectiveArgsAreKnown()
+    public function testDirectiveArgsAreKnown() : void
     {
         $this->expectPassesRule(new KnownArgumentNames, '
       {
@@ -105,7 +105,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('undirective args are invalid')
      */
-    public function testUndirectiveArgsAreInvalid()
+    public function testUndirectiveArgsAreInvalid() : void
     {
         $this->expectFailsRule(new KnownArgumentNames, '
       {
@@ -119,7 +119,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('misspelled directive args are reported')
      */
-    public function testMisspelledDirectiveArgsAreReported()
+    public function testMisspelledDirectiveArgsAreReported() : void
     {
         $this->expectFailsRule(new KnownArgumentNames, '
       {
@@ -133,7 +133,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('invalid arg name')
      */
-    public function testInvalidArgName()
+    public function testInvalidArgName() : void
     {
         $this->expectFailsRule(new KnownArgumentNames, '
       fragment invalidArgName on Dog {
@@ -147,7 +147,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('misspelled arg name is reported')
      */
-    public function testMisspelledArgNameIsReported()
+    public function testMisspelledArgNameIsReported() : void
     {
         $this->expectFailsRule(new KnownArgumentNames, '
       fragment invalidArgName on Dog {
@@ -161,7 +161,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('unknown args amongst known args')
      */
-    public function testUnknownArgsAmongstKnownArgs()
+    public function testUnknownArgsAmongstKnownArgs() : void
     {
         $this->expectFailsRule(new KnownArgumentNames, '
       fragment oneGoodArgOneInvalidArg on Dog {
@@ -176,7 +176,7 @@ class KnownArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('unknown args deeply')
      */
-    public function testUnknownArgsDeeply()
+    public function testUnknownArgsDeeply() : void
     {
         $this->expectFailsRule(new KnownArgumentNames, '
       {
diff --git a/tests/Validator/KnownDirectivesTest.php b/tests/Validator/KnownDirectivesTest.php
index 5347ec7..7f9fd39 100644
--- a/tests/Validator/KnownDirectivesTest.php
+++ b/tests/Validator/KnownDirectivesTest.php
@@ -12,7 +12,7 @@ class KnownDirectivesTest extends ValidatorTestCase
     /**
      * @see it('with no directives')
      */
-    public function testWithNoDirectives()
+    public function testWithNoDirectives() : void
     {
         $this->expectPassesRule(new KnownDirectives, '
       query Foo {
@@ -29,7 +29,7 @@ class KnownDirectivesTest extends ValidatorTestCase
     /**
      * @see it('with known directives')
      */
-    public function testWithKnownDirectives()
+    public function testWithKnownDirectives() : void
     {
         $this->expectPassesRule(new KnownDirectives, '
       {
@@ -46,7 +46,7 @@ class KnownDirectivesTest extends ValidatorTestCase
     /**
      * @see it('with unknown directive')
      */
-    public function testWithUnknownDirective()
+    public function testWithUnknownDirective() : void
     {
         $this->expectFailsRule(new KnownDirectives, '
       {
@@ -62,7 +62,7 @@ class KnownDirectivesTest extends ValidatorTestCase
     /**
      * @see it('with many unknown directives')
      */
-    public function testWithManyUnknownDirectives()
+    public function testWithManyUnknownDirectives() : void
     {
         $this->expectFailsRule(new KnownDirectives, '
       {
@@ -86,7 +86,7 @@ class KnownDirectivesTest extends ValidatorTestCase
     /**
      * @see it('with well placed directives')
      */
-    public function testWithWellPlacedDirectives()
+    public function testWithWellPlacedDirectives() : void
     {
         $this->expectPassesRule(new KnownDirectives, '
       query Foo @onQuery {
@@ -105,7 +105,7 @@ class KnownDirectivesTest extends ValidatorTestCase
     /**
      * @see it('with misplaced directives')
      */
-    public function testWithMisplacedDirectives()
+    public function testWithMisplacedDirectives() : void
     {
         $this->expectFailsRule(new KnownDirectives, '
       query Foo @include(if: true) {
@@ -129,7 +129,7 @@ class KnownDirectivesTest extends ValidatorTestCase
     /**
      * @see it('with well placed directives')
      */
-    public function testWSLWithWellPlacedDirectives()
+    public function testWSLWithWellPlacedDirectives() : void
     {
         $this->expectPassesRule(new KnownDirectives, '
         type MyObj implements MyInterface @onObject {
@@ -173,7 +173,7 @@ class KnownDirectivesTest extends ValidatorTestCase
     /**
      * @see it('with misplaced directives')
      */
-    public function testWSLWithMisplacedDirectives()
+    public function testWSLWithMisplacedDirectives() : void
     {
         $this->expectFailsRule(new KnownDirectives, '
         type MyObj implements MyInterface @onInterface {
diff --git a/tests/Validator/KnownFragmentNamesTest.php b/tests/Validator/KnownFragmentNamesTest.php
index 65fd24d..5764150 100644
--- a/tests/Validator/KnownFragmentNamesTest.php
+++ b/tests/Validator/KnownFragmentNamesTest.php
@@ -12,7 +12,7 @@ class KnownFragmentNamesTest extends ValidatorTestCase
     /**
      * @see it('known fragment names are valid')
      */
-    public function testKnownFragmentNamesAreValid()
+    public function testKnownFragmentNamesAreValid() : void
     {
         $this->expectPassesRule(new KnownFragmentNames, '
       {
@@ -39,7 +39,7 @@ class KnownFragmentNamesTest extends ValidatorTestCase
     /**
      * @see it('unknown fragment names are invalid')
      */
-    public function testUnknownFragmentNamesAreInvalid()
+    public function testUnknownFragmentNamesAreInvalid() : void
     {
         $this->expectFailsRule(new KnownFragmentNames, '
       {
diff --git a/tests/Validator/KnownTypeNamesTest.php b/tests/Validator/KnownTypeNamesTest.php
index 322a361..9604cb8 100644
--- a/tests/Validator/KnownTypeNamesTest.php
+++ b/tests/Validator/KnownTypeNamesTest.php
@@ -12,7 +12,7 @@ class KnownTypeNamesTest extends ValidatorTestCase
     /**
      * @see it('known type names are valid')
      */
-    public function testKnownTypeNamesAreValid()
+    public function testKnownTypeNamesAreValid() : void
     {
         $this->expectPassesRule(new KnownTypeNames, '
       query Foo($var: String, $required: [String!]!) {
@@ -29,7 +29,7 @@ class KnownTypeNamesTest extends ValidatorTestCase
     /**
      * @see it('unknown type names are invalid')
      */
-    public function testUnknownTypeNamesAreInvalid()
+    public function testUnknownTypeNamesAreInvalid() : void
     {
         $this->expectFailsRule(new KnownTypeNames, '
       query Foo($var: JumbledUpLetters) {
@@ -51,7 +51,7 @@ class KnownTypeNamesTest extends ValidatorTestCase
     /**
      * @see it('ignores type definitions')
      */
-    public function testIgnoresTypeDefinitions()
+    public function testIgnoresTypeDefinitions() : void
     {
         $this->expectFailsRule(new KnownTypeNames, '
       type NotInTheSchema {
diff --git a/tests/Validator/LoneAnonymousOperationTest.php b/tests/Validator/LoneAnonymousOperationTest.php
index e7efb83..e8540c8 100644
--- a/tests/Validator/LoneAnonymousOperationTest.php
+++ b/tests/Validator/LoneAnonymousOperationTest.php
@@ -12,7 +12,7 @@ class LoneAnonymousOperationTest extends ValidatorTestCase
     /**
      * @see it('no operations')
      */
-    public function testNoOperations()
+    public function testNoOperations() : void
     {
         $this->expectPassesRule(new LoneAnonymousOperation, '
       fragment fragA on Type {
@@ -24,7 +24,7 @@ class LoneAnonymousOperationTest extends ValidatorTestCase
     /**
      * @see it('one anon operation')
      */
-    public function testOneAnonOperation()
+    public function testOneAnonOperation() : void
     {
         $this->expectPassesRule(new LoneAnonymousOperation, '
       {
@@ -36,7 +36,7 @@ class LoneAnonymousOperationTest extends ValidatorTestCase
     /**
      * @see it('multiple named operations')
      */
-    public function testMultipleNamedOperations()
+    public function testMultipleNamedOperations() : void
     {
         $this->expectPassesRule(new LoneAnonymousOperation, '
       query Foo {
@@ -52,7 +52,7 @@ class LoneAnonymousOperationTest extends ValidatorTestCase
     /**
      * @see it('anon operation with fragment')
      */
-    public function testAnonOperationWithFragment()
+    public function testAnonOperationWithFragment() : void
     {
         $this->expectPassesRule(new LoneAnonymousOperation, '
       {
@@ -67,7 +67,7 @@ class LoneAnonymousOperationTest extends ValidatorTestCase
     /**
      * @see it('multiple anon operations')
      */
-    public function testMultipleAnonOperations()
+    public function testMultipleAnonOperations() : void
     {
         $this->expectFailsRule(new LoneAnonymousOperation, '
       {
@@ -85,7 +85,7 @@ class LoneAnonymousOperationTest extends ValidatorTestCase
     /**
      * @see it('anon operation with a mutation')
      */
-    public function testAnonOperationWithMutation()
+    public function testAnonOperationWithMutation() : void
     {
         $this->expectFailsRule(new LoneAnonymousOperation, '
       {
@@ -102,7 +102,7 @@ class LoneAnonymousOperationTest extends ValidatorTestCase
     /**
      * @see it('anon operation with a subscription')
      */
-    public function testAnonOperationWithSubscription()
+    public function testAnonOperationWithSubscription() : void
     {
         $this->expectFailsRule(new LoneAnonymousOperation, '
       {
diff --git a/tests/Validator/NoFragmentCyclesTest.php b/tests/Validator/NoFragmentCyclesTest.php
index 1df42fd..a962dc3 100644
--- a/tests/Validator/NoFragmentCyclesTest.php
+++ b/tests/Validator/NoFragmentCyclesTest.php
@@ -12,7 +12,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('single reference is valid')
      */
-    public function testSingleReferenceIsValid()
+    public function testSingleReferenceIsValid() : void
     {
         $this->expectPassesRule(new NoFragmentCycles(), '
       fragment fragA on Dog { ...fragB }
@@ -23,7 +23,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('spreading twice is not circular')
      */
-    public function testSpreadingTwiceIsNotCircular()
+    public function testSpreadingTwiceIsNotCircular() : void
     {
         $this->expectPassesRule(new NoFragmentCycles, '
       fragment fragA on Dog { ...fragB, ...fragB }
@@ -34,7 +34,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('spreading twice indirectly is not circular')
      */
-    public function testSpreadingTwiceIndirectlyIsNotCircular()
+    public function testSpreadingTwiceIndirectlyIsNotCircular() : void
     {
         $this->expectPassesRule(new NoFragmentCycles, '
       fragment fragA on Dog { ...fragB, ...fragC }
@@ -46,7 +46,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('double spread within abstract types')
      */
-    public function testDoubleSpreadWithinAbstractTypes()
+    public function testDoubleSpreadWithinAbstractTypes() : void
     {
         $this->expectPassesRule(new NoFragmentCycles, '
       fragment nameFragment on Pet {
@@ -64,7 +64,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('does not false positive on unknown fragment')
      */
-    public function testDoesNotFalsePositiveOnUnknownFragment()
+    public function testDoesNotFalsePositiveOnUnknownFragment() : void
     {
         $this->expectPassesRule(new NoFragmentCycles, '
       fragment nameFragment on Pet {
@@ -76,7 +76,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('spreading recursively within field fails')
      */
-    public function testSpreadingRecursivelyWithinFieldFails()
+    public function testSpreadingRecursivelyWithinFieldFails() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragA on Human { relatives { ...fragA } },
@@ -88,7 +88,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('no spreading itself directly')
      */
-    public function testNoSpreadingItselfDirectly()
+    public function testNoSpreadingItselfDirectly() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragA on Dog { ...fragA }
@@ -100,7 +100,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('no spreading itself directly within inline fragment')
      */
-    public function testNoSpreadingItselfDirectlyWithinInlineFragment()
+    public function testNoSpreadingItselfDirectlyWithinInlineFragment() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragA on Pet {
@@ -116,7 +116,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('no spreading itself indirectly')
      */
-    public function testNoSpreadingItselfIndirectly()
+    public function testNoSpreadingItselfIndirectly() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragA on Dog { ...fragB }
@@ -132,7 +132,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('no spreading itself indirectly reports opposite order')
      */
-    public function testNoSpreadingItselfIndirectlyReportsOppositeOrder()
+    public function testNoSpreadingItselfIndirectlyReportsOppositeOrder() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragB on Dog { ...fragA }
@@ -148,7 +148,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('no spreading itself indirectly within inline fragment')
      */
-    public function testNoSpreadingItselfIndirectlyWithinInlineFragment()
+    public function testNoSpreadingItselfIndirectlyWithinInlineFragment() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragA on Pet {
@@ -172,7 +172,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('no spreading itself deeply')
      */
-    public function testNoSpreadingItselfDeeply()
+    public function testNoSpreadingItselfDeeply() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragA on Dog { ...fragB }
@@ -210,7 +210,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('no spreading itself deeply two paths')
      */
-    public function testNoSpreadingItselfDeeplyTwoPaths()
+    public function testNoSpreadingItselfDeeplyTwoPaths() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragA on Dog { ...fragB, ...fragC }
@@ -231,7 +231,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('no spreading itself deeply two paths -- alt traverse order')
      */
-    public function testNoSpreadingItselfDeeplyTwoPathsTraverseOrder()
+    public function testNoSpreadingItselfDeeplyTwoPathsTraverseOrder() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragA on Dog { ...fragC }
@@ -252,7 +252,7 @@ class NoFragmentCyclesTest extends ValidatorTestCase
     /**
      * @see it('no spreading itself deeply and immediately')
      */
-    public function testNoSpreadingItselfDeeplyAndImmediately()
+    public function testNoSpreadingItselfDeeplyAndImmediately() : void
     {
         $this->expectFailsRule(new NoFragmentCycles, '
       fragment fragA on Dog { ...fragB }
diff --git a/tests/Validator/NoUndefinedVariablesTest.php b/tests/Validator/NoUndefinedVariablesTest.php
index 4df41c5..b4b56b3 100644
--- a/tests/Validator/NoUndefinedVariablesTest.php
+++ b/tests/Validator/NoUndefinedVariablesTest.php
@@ -12,7 +12,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('all variables defined')
      */
-    public function testAllVariablesDefined()
+    public function testAllVariablesDefined() : void
     {
         $this->expectPassesRule(new NoUndefinedVariables(), '
       query Foo($a: String, $b: String, $c: String) {
@@ -24,7 +24,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('all variables deeply defined')
      */
-    public function testAllVariablesDeeplyDefined()
+    public function testAllVariablesDeeplyDefined() : void
     {
         $this->expectPassesRule(new NoUndefinedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -40,7 +40,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('all variables deeply in inline fragments defined')
      */
-    public function testAllVariablesDeeplyInInlineFragmentsDefined()
+    public function testAllVariablesDeeplyInInlineFragmentsDefined() : void
     {
         $this->expectPassesRule(new NoUndefinedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -60,7 +60,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('all variables in fragments deeply defined')
      */
-    public function testAllVariablesInFragmentsDeeplyDefined()
+    public function testAllVariablesInFragmentsDeeplyDefined() : void
     {
         $this->expectPassesRule(new NoUndefinedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -85,7 +85,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable within single fragment defined in multiple operations')
      */
-    public function testVariableWithinSingleFragmentDefinedInMultipleOperations()
+    public function testVariableWithinSingleFragmentDefinedInMultipleOperations() : void
     {
         // variable within single fragment defined in multiple operations
         $this->expectPassesRule(new NoUndefinedVariables, '
@@ -104,7 +104,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable within fragments defined in operations')
      */
-    public function testVariableWithinFragmentsDefinedInOperations()
+    public function testVariableWithinFragmentsDefinedInOperations() : void
     {
         $this->expectPassesRule(new NoUndefinedVariables, '
       query Foo($a: String) {
@@ -125,7 +125,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable within recursive fragment defined')
      */
-    public function testVariableWithinRecursiveFragmentDefined()
+    public function testVariableWithinRecursiveFragmentDefined() : void
     {
         $this->expectPassesRule(new NoUndefinedVariables, '
       query Foo($a: String) {
@@ -142,7 +142,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable not defined')
      */
-    public function testVariableNotDefined()
+    public function testVariableNotDefined() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -156,7 +156,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable not defined by un-named query')
      */
-    public function testVariableNotDefinedByUnNamedQuery()
+    public function testVariableNotDefinedByUnNamedQuery() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       {
@@ -170,7 +170,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('multiple variables not defined')
      */
-    public function testMultipleVariablesNotDefined()
+    public function testMultipleVariablesNotDefined() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       query Foo($b: String) {
@@ -185,7 +185,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable in fragment not defined by un-named query')
      */
-    public function testVariableInFragmentNotDefinedByUnNamedQuery()
+    public function testVariableInFragmentNotDefinedByUnNamedQuery() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       {
@@ -202,7 +202,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable in fragment not defined by operation')
      */
-    public function testVariableInFragmentNotDefinedByOperation()
+    public function testVariableInFragmentNotDefinedByOperation() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       query Foo($a: String, $b: String) {
@@ -229,7 +229,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('multiple variables in fragments not defined')
      */
-    public function testMultipleVariablesInFragmentsNotDefined()
+    public function testMultipleVariablesInFragmentsNotDefined() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       query Foo($b: String) {
@@ -257,7 +257,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('single variable in fragment not defined by multiple operations')
      */
-    public function testSingleVariableInFragmentNotDefinedByMultipleOperations()
+    public function testSingleVariableInFragmentNotDefinedByMultipleOperations() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       query Foo($a: String) {
@@ -278,7 +278,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variables in fragment not defined by multiple operations')
      */
-    public function testVariablesInFragmentNotDefinedByMultipleOperations()
+    public function testVariablesInFragmentNotDefinedByMultipleOperations() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       query Foo($b: String) {
@@ -299,7 +299,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable in fragment used by other operation')
      */
-    public function testVariableInFragmentUsedByOtherOperation()
+    public function testVariableInFragmentUsedByOtherOperation() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       query Foo($b: String) {
@@ -323,7 +323,7 @@ class NoUndefinedVariablesTest extends ValidatorTestCase
     /**
      * @see it('multiple undefined variables produce multiple errors')
      */
-    public function testMultipleUndefinedVariablesProduceMultipleErrors()
+    public function testMultipleUndefinedVariablesProduceMultipleErrors() : void
     {
         $this->expectFailsRule(new NoUndefinedVariables, '
       query Foo($b: String) {
diff --git a/tests/Validator/NoUnusedFragmentsTest.php b/tests/Validator/NoUnusedFragmentsTest.php
index d297621..323f915 100644
--- a/tests/Validator/NoUnusedFragmentsTest.php
+++ b/tests/Validator/NoUnusedFragmentsTest.php
@@ -12,7 +12,7 @@ class NoUnusedFragmentsTest extends ValidatorTestCase
     /**
      * @see it('all fragment names are used')
      */
-    public function testAllFragmentNamesAreUsed()
+    public function testAllFragmentNamesAreUsed() : void
     {
         $this->expectPassesRule(new NoUnusedFragments(), '
       {
@@ -39,7 +39,7 @@ class NoUnusedFragmentsTest extends ValidatorTestCase
     /**
      * @see it('all fragment names are used by multiple operations')
      */
-    public function testAllFragmentNamesAreUsedByMultipleOperations()
+    public function testAllFragmentNamesAreUsedByMultipleOperations() : void
     {
         $this->expectPassesRule(new NoUnusedFragments, '
       query Foo {
@@ -68,7 +68,7 @@ class NoUnusedFragmentsTest extends ValidatorTestCase
     /**
      * @see it('contains unknown fragments')
      */
-    public function testContainsUnknownFragments()
+    public function testContainsUnknownFragments() : void
     {
         $this->expectFailsRule(new NoUnusedFragments, '
       query Foo {
@@ -106,7 +106,7 @@ class NoUnusedFragmentsTest extends ValidatorTestCase
     /**
      * @see it('contains unknown fragments with ref cycle')
      */
-    public function testContainsUnknownFragmentsWithRefCycle()
+    public function testContainsUnknownFragmentsWithRefCycle() : void
     {
         $this->expectFailsRule(new NoUnusedFragments, '
       query Foo {
@@ -146,7 +146,7 @@ class NoUnusedFragmentsTest extends ValidatorTestCase
     /**
      * @see it('contains unknown and undef fragments')
      */
-    public function testContainsUnknownAndUndefFragments()
+    public function testContainsUnknownAndUndefFragments() : void
     {
 
         $this->expectFailsRule(new NoUnusedFragments, '
diff --git a/tests/Validator/NoUnusedVariablesTest.php b/tests/Validator/NoUnusedVariablesTest.php
index 9d3b3a9..c261c15 100644
--- a/tests/Validator/NoUnusedVariablesTest.php
+++ b/tests/Validator/NoUnusedVariablesTest.php
@@ -12,7 +12,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('uses all variables')
      */
-    public function testUsesAllVariables()
+    public function testUsesAllVariables() : void
     {
         $this->expectPassesRule(new NoUnusedVariables(), '
       query Foo($a: String, $b: String, $c: String) {
@@ -24,7 +24,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('uses all variables deeply')
      */
-    public function testUsesAllVariablesDeeply()
+    public function testUsesAllVariablesDeeply() : void
     {
         $this->expectPassesRule(new NoUnusedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -40,7 +40,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('uses all variables deeply in inline fragments')
      */
-    public function testUsesAllVariablesDeeplyInInlineFragments()
+    public function testUsesAllVariablesDeeplyInInlineFragments() : void
     {
         $this->expectPassesRule(new NoUnusedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -60,7 +60,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('uses all variables in fragments')
      */
-    public function testUsesAllVariablesInFragments()
+    public function testUsesAllVariablesInFragments() : void
     {
         $this->expectPassesRule(new NoUnusedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -85,7 +85,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable used by fragment in multiple operations')
      */
-    public function testVariableUsedByFragmentInMultipleOperations()
+    public function testVariableUsedByFragmentInMultipleOperations() : void
     {
         $this->expectPassesRule(new NoUnusedVariables, '
       query Foo($a: String) {
@@ -106,7 +106,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable used by recursive fragment')
      */
-    public function testVariableUsedByRecursiveFragment()
+    public function testVariableUsedByRecursiveFragment() : void
     {
         $this->expectPassesRule(new NoUnusedVariables, '
       query Foo($a: String) {
@@ -123,7 +123,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable not used')
      */
-    public function testVariableNotUsed()
+    public function testVariableNotUsed() : void
     {
         $this->expectFailsRule(new NoUnusedVariables, '
       query ($a: String, $b: String, $c: String) {
@@ -137,7 +137,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('multiple variables not used')
      */
-    public function testMultipleVariablesNotUsed()
+    public function testMultipleVariablesNotUsed() : void
     {
         $this->expectFailsRule(new NoUnusedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -152,7 +152,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable not used in fragments')
      */
-    public function testVariableNotUsedInFragments()
+    public function testVariableNotUsedInFragments() : void
     {
         $this->expectFailsRule(new NoUnusedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -179,7 +179,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('multiple variables not used')
      */
-    public function testMultipleVariablesNotUsed2()
+    public function testMultipleVariablesNotUsed2() : void
     {
         $this->expectFailsRule(new NoUnusedVariables, '
       query Foo($a: String, $b: String, $c: String) {
@@ -207,7 +207,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable not used by unreferenced fragment')
      */
-    public function testVariableNotUsedByUnreferencedFragment()
+    public function testVariableNotUsedByUnreferencedFragment() : void
     {
         $this->expectFailsRule(new NoUnusedVariables, '
       query Foo($b: String) {
@@ -227,7 +227,7 @@ class NoUnusedVariablesTest extends ValidatorTestCase
     /**
      * @see it('variable not used by fragment used by other operation')
      */
-    public function testVariableNotUsedByFragmentUsedByOtherOperation()
+    public function testVariableNotUsedByFragmentUsedByOtherOperation() : void
     {
         $this->expectFailsRule(new NoUnusedVariables, '
       query Foo($b: String) {
diff --git a/tests/Validator/OverlappingFieldsCanBeMergedTest.php b/tests/Validator/OverlappingFieldsCanBeMergedTest.php
index df20cf8..2aaed7e 100644
--- a/tests/Validator/OverlappingFieldsCanBeMergedTest.php
+++ b/tests/Validator/OverlappingFieldsCanBeMergedTest.php
@@ -16,7 +16,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('unique fields')
      */
-    public function testUniqueFields()
+    public function testUniqueFields() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged(), '
       fragment uniqueFields on Dog {
@@ -29,7 +29,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('identical fields')
      */
-    public function testIdenticalFields()
+    public function testIdenticalFields() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged, '
       fragment mergeIdenticalFields on Dog {
@@ -42,7 +42,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('identical fields with identical args')
      */
-    public function testIdenticalFieldsWithIdenticalArgs()
+    public function testIdenticalFieldsWithIdenticalArgs() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged, '
       fragment mergeIdenticalFieldsWithIdenticalArgs on Dog {
@@ -55,7 +55,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('identical fields with identical directives')
      */
-    public function testIdenticalFieldsWithIdenticalDirectives()
+    public function testIdenticalFieldsWithIdenticalDirectives() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged, '
       fragment mergeSameFieldsWithSameDirectives on Dog {
@@ -68,7 +68,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('different args with different aliases')
      */
-    public function testDifferentArgsWithDifferentAliases()
+    public function testDifferentArgsWithDifferentAliases() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged, '
       fragment differentArgsWithDifferentAliases on Dog {
@@ -81,7 +81,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('different directives with different aliases')
      */
-    public function testDifferentDirectivesWithDifferentAliases()
+    public function testDifferentDirectivesWithDifferentAliases() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged, '
       fragment differentDirectivesWithDifferentAliases on Dog {
@@ -94,7 +94,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('different skip/include directives accepted')
      */
-    public function testDifferentSkipIncludeDirectivesAccepted()
+    public function testDifferentSkipIncludeDirectivesAccepted() : void
     {
         // Note: Differing skip/include directives don't create an ambiguous return
         // value and are acceptable in conditions where differing runtime values
@@ -110,7 +110,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('Same aliases with different field targets')
      */
-    public function testSameAliasesWithDifferentFieldTargets()
+    public function testSameAliasesWithDifferentFieldTargets() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       fragment sameAliasesWithDifferentFieldTargets on Dog {
@@ -128,7 +128,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('Same aliases allowed on non-overlapping fields')
      */
-    public function testSameAliasesAllowedOnNonOverlappingFields()
+    public function testSameAliasesAllowedOnNonOverlappingFields() : void
     {
         // This is valid since no object can be both a "Dog" and a "Cat", thus
         // these fields can never overlap.
@@ -147,7 +147,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('Alias masking direct field access')
      */
-    public function testAliasMaskingDirectFieldAccess()
+    public function testAliasMaskingDirectFieldAccess() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       fragment aliasMaskingDirectFieldAccess on Dog {
@@ -165,7 +165,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('different args, second adds an argument')
      */
-    public function testDifferentArgsSecondAddsAnArgument()
+    public function testDifferentArgsSecondAddsAnArgument() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       fragment conflictingArgs on Dog {
@@ -183,7 +183,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('different args, second missing an argument')
      */
-    public function testDifferentArgsSecondMissingAnArgument()
+    public function testDifferentArgsSecondMissingAnArgument() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       fragment conflictingArgs on Dog {
@@ -203,7 +203,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('conflicting args')
      */
-    public function testConflictingArgs()
+    public function testConflictingArgs() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       fragment conflictingArgs on Dog {
@@ -221,7 +221,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('allows different args where no conflict is possible')
      */
-    public function testAllowsDifferentArgsWhereNoConflictIsPossible()
+    public function testAllowsDifferentArgsWhereNoConflictIsPossible() : void
     {
         // This is valid since no object can be both a "Dog" and a "Cat", thus
         // these fields can never overlap.
@@ -240,7 +240,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('encounters conflict in fragments')
      */
-    public function testEncountersConflictInFragments()
+    public function testEncountersConflictInFragments() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       {
@@ -264,7 +264,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('reports each conflict once')
      */
-    public function testReportsEachConflictOnce()
+    public function testReportsEachConflictOnce() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       {
@@ -307,7 +307,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('deep conflict')
      */
-    public function testDeepConflict()
+    public function testDeepConflict() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       {
@@ -334,7 +334,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('deep conflict with multiple issues')
      */
-    public function testDeepConflictWithMultipleIssues()
+    public function testDeepConflictWithMultipleIssues() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       {
@@ -368,7 +368,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('very deep conflict')
      */
-    public function testVeryDeepConflict()
+    public function testVeryDeepConflict() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       {
@@ -401,7 +401,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('reports deep conflict to nearest common ancestor')
      */
-    public function testReportsDeepConflictToNearestCommonAncestor()
+    public function testReportsDeepConflictToNearestCommonAncestor() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       {
@@ -435,7 +435,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('reports deep conflict to nearest common ancestor in fragments')
      */
-    public function testReportsDeepConflictToNearestCommonAncestorInFragments()
+    public function testReportsDeepConflictToNearestCommonAncestorInFragments() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       {
@@ -477,7 +477,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('reports deep conflict in nested fragments')
      */
-    public function testReportsDeepConflictInNestedFragments()
+    public function testReportsDeepConflictInNestedFragments() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       {
@@ -523,7 +523,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('ignores unknown fragments')
      */
-    public function testIgnoresUnknownFragments()
+    public function testIgnoresUnknownFragments() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged, '
       {
@@ -544,7 +544,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('conflicting return types which potentially overlap')
      */
-    public function testConflictingReturnTypesWhichPotentiallyOverlap()
+    public function testConflictingReturnTypesWhichPotentiallyOverlap() : void
     {
         // This is invalid since an object could potentially be both the Object
         // type IntBox and the interface type NonNullStringBox1. While that
@@ -576,7 +576,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('compatible return shapes on different return types')
      */
-    public function testCompatibleReturnShapesOnDifferentReturnTypes()
+    public function testCompatibleReturnShapesOnDifferentReturnTypes() : void
     {
         // In this case `deepBox` returns `SomeBox` in the first usage, and
         // `StringBox` in the second usage. These return types are not the same!
@@ -602,7 +602,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('disallows differing return types despite no overlap')
      */
-    public function testDisallowsDifferingReturnTypesDespiteNoOverlap()
+    public function testDisallowsDifferingReturnTypesDespiteNoOverlap() : void
     {
         $this->expectFailsRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -630,7 +630,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('reports correctly when a non-exclusive follows an exclusive')
      */
-    public function testReportsCorrectlyWhenANonExclusiveFollowsAnExclusive()
+    public function testReportsCorrectlyWhenANonExclusiveFollowsAnExclusive() : void
     {
         $this->expectFailsRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -694,7 +694,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('disallows differing return type nullability despite no overlap')
      */
-    public function testDisallowsDifferingReturnTypeNullabilityDespiteNoOverlap()
+    public function testDisallowsDifferingReturnTypeNullabilityDespiteNoOverlap() : void
     {
         $this->expectFailsRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -722,7 +722,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('disallows differing return type list despite no overlap')
      */
-    public function testDisallowsDifferingReturnTypeListDespiteNoOverlap()
+    public function testDisallowsDifferingReturnTypeListDespiteNoOverlap() : void
     {
         $this->expectFailsRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -778,7 +778,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
       ]);
     }
 
-    public function testDisallowsDifferingSubfields()
+    public function testDisallowsDifferingSubfields() : void
     {
         $this->expectFailsRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -812,7 +812,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('disallows differing deep return types despite no overlap')
      */
-    public function testDisallowsDifferingDeepReturnTypesDespiteNoOverlap()
+    public function testDisallowsDifferingDeepReturnTypesDespiteNoOverlap() : void
     {
         $this->expectFailsRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -848,7 +848,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('allows non-conflicting overlaping types')
      */
-    public function testAllowsNonConflictingOverlapingTypes()
+    public function testAllowsNonConflictingOverlapingTypes() : void
     {
         $this->expectPassesRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -867,7 +867,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('same wrapped scalar return types')
      */
-    public function testSameWrappedScalarReturnTypes()
+    public function testSameWrappedScalarReturnTypes() : void
     {
         $this->expectPassesRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -886,7 +886,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('allows inline typeless fragments')
      */
-    public function testAllowsInlineTypelessFragments()
+    public function testAllowsInlineTypelessFragments() : void
     {
         $this->expectPassesRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -901,7 +901,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('compares deep types including list')
      */
-    public function testComparesDeepTypesIncludingList()
+    public function testComparesDeepTypesIncludingList() : void
     {
         $this->expectFailsRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -940,7 +940,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('ignores unknown types')
      */
-    public function testIgnoresUnknownTypes()
+    public function testIgnoresUnknownTypes() : void
     {
         $this->expectPassesRuleWithSchema($this->getSchema(), new OverlappingFieldsCanBeMerged, '
         {
@@ -959,7 +959,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('error message contains hint for alias conflict')
      */
-    public function testErrorMessageContainsHintForAliasConflict()
+    public function testErrorMessageContainsHintForAliasConflict() : void
     {
         // The error template should end with a hint for the user to try using
         // different aliases.
@@ -972,7 +972,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('does not infinite loop on recursive fragment')
      */
-    public function testDoesNotInfiniteLoopOnRecursiveFragment()
+    public function testDoesNotInfiniteLoopOnRecursiveFragment() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged, '
         fragment fragA on Human { name, relatives { name, ...fragA } }
@@ -982,7 +982,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('does not infinite loop on immediately recursive fragment')
      */
-    public function testDoesNotInfiniteLoopOnImmeditelyRecursiveFragment()
+    public function testDoesNotInfiniteLoopOnImmeditelyRecursiveFragment() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged, '
         fragment fragA on Human { name, ...fragA }
@@ -992,7 +992,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('does not infinite loop on transitively recursive fragment')
      */
-    public function testDoesNotInfiniteLoopOnTransitivelyRecursiveFragment()
+    public function testDoesNotInfiniteLoopOnTransitivelyRecursiveFragment() : void
     {
         $this->expectPassesRule(new OverlappingFieldsCanBeMerged, '
         fragment fragA on Human { name, ...fragB }
@@ -1004,7 +1004,7 @@ class OverlappingFieldsCanBeMergedTest extends ValidatorTestCase
     /**
      * @see it('find invalid case even with immediately recursive fragment')
      */
-    public function testFindInvalidCaseEvenWithImmediatelyRecursiveFragment()
+    public function testFindInvalidCaseEvenWithImmediatelyRecursiveFragment() : void
     {
         $this->expectFailsRule(new OverlappingFieldsCanBeMerged, '
       fragment sameAliasesWithDifferentFieldTargets on Dob {
diff --git a/tests/Validator/PossibleFragmentSpreadsTest.php b/tests/Validator/PossibleFragmentSpreadsTest.php
index 129ffa9..f5f074b 100644
--- a/tests/Validator/PossibleFragmentSpreadsTest.php
+++ b/tests/Validator/PossibleFragmentSpreadsTest.php
@@ -12,7 +12,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('of the same object')
      */
-    public function testOfTheSameObject()
+    public function testOfTheSameObject() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads(), '
       fragment objectWithinObject on Dog { ...dogFragment }
@@ -23,7 +23,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('of the same object with inline fragment')
      */
-    public function testOfTheSameObjectWithInlineFragment()
+    public function testOfTheSameObjectWithInlineFragment() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment objectWithinObjectAnon on Dog { ... on Dog { barkVolume } }
@@ -33,7 +33,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('object into an implemented interface')
      */
-    public function testObjectIntoAnImplementedInterface()
+    public function testObjectIntoAnImplementedInterface() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment objectWithinInterface on Pet { ...dogFragment }
@@ -44,7 +44,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('object into containing union')
      */
-    public function testObjectIntoContainingUnion()
+    public function testObjectIntoContainingUnion() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment objectWithinUnion on CatOrDog { ...dogFragment }
@@ -55,7 +55,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('union into contained object')
      */
-    public function testUnionIntoContainedObject()
+    public function testUnionIntoContainedObject() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment unionWithinObject on Dog { ...catOrDogFragment }
@@ -66,7 +66,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('union into overlapping interface')
      */
-    public function testUnionIntoOverlappingInterface()
+    public function testUnionIntoOverlappingInterface() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment unionWithinInterface on Pet { ...catOrDogFragment }
@@ -77,7 +77,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('union into overlapping union')
      */
-    public function testUnionIntoOverlappingUnion()
+    public function testUnionIntoOverlappingUnion() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment unionWithinUnion on DogOrHuman { ...catOrDogFragment }
@@ -88,7 +88,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('interface into implemented object')
      */
-    public function testInterfaceIntoImplementedObject()
+    public function testInterfaceIntoImplementedObject() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment interfaceWithinObject on Dog { ...petFragment }
@@ -99,7 +99,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('interface into overlapping interface')
      */
-    public function testInterfaceIntoOverlappingInterface()
+    public function testInterfaceIntoOverlappingInterface() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment interfaceWithinInterface on Pet { ...beingFragment }
@@ -110,7 +110,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('interface into overlapping interface in inline fragment')
      */
-    public function testInterfaceIntoOverlappingInterfaceInInlineFragment()
+    public function testInterfaceIntoOverlappingInterfaceInInlineFragment() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment interfaceWithinInterface on Pet { ... on Being { name } }
@@ -120,7 +120,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('interface into overlapping union')
      */
-    public function testInterfaceIntoOverlappingUnion()
+    public function testInterfaceIntoOverlappingUnion() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment interfaceWithinUnion on CatOrDog { ...petFragment }
@@ -131,7 +131,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('ignores incorrect type (caught by FragmentsOnCompositeTypes)')
      */
-    public function testIgnoresIncorrectTypeCaughtByFragmentsOnCompositeTypes()
+    public function testIgnoresIncorrectTypeCaughtByFragmentsOnCompositeTypes() : void
     {
         $this->expectPassesRule(new PossibleFragmentSpreads, '
       fragment petFragment on Pet { ...badInADifferentWay }
@@ -142,7 +142,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('different object into object')
      */
-    public function testDifferentObjectIntoObject()
+    public function testDifferentObjectIntoObject() : void
     {
         $this->expectFailsRule(new PossibleFragmentSpreads, '
       fragment invalidObjectWithinObject on Cat { ...dogFragment }
@@ -155,7 +155,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('different object into object in inline fragment')
      */
-    public function testDifferentObjectIntoObjectInInlineFragment()
+    public function testDifferentObjectIntoObjectInInlineFragment() : void
     {
         $this->expectFailsRule(new PossibleFragmentSpreads, '
       fragment invalidObjectWithinObjectAnon on Cat {
@@ -169,7 +169,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('object into not implementing interface')
      */
-    public function testObjectIntoNotImplementingInterface()
+    public function testObjectIntoNotImplementingInterface() : void
     {
         $this->expectFailsRule(new PossibleFragmentSpreads, '
       fragment invalidObjectWithinInterface on Pet { ...humanFragment }
@@ -182,7 +182,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('object into not containing union')
      */
-    public function testObjectIntoNotContainingUnion()
+    public function testObjectIntoNotContainingUnion() : void
     {
         $this->expectFailsRule(new PossibleFragmentSpreads, '
       fragment invalidObjectWithinUnion on CatOrDog { ...humanFragment }
@@ -195,7 +195,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('union into not contained object')
      */
-    public function testUnionIntoNotContainedObject()
+    public function testUnionIntoNotContainedObject() : void
     {
         $this->expectFailsRule(new PossibleFragmentSpreads, '
       fragment invalidUnionWithinObject on Human { ...catOrDogFragment }
@@ -208,7 +208,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('union into non overlapping interface')
      */
-    public function testUnionIntoNonOverlappingInterface()
+    public function testUnionIntoNonOverlappingInterface() : void
     {
         $this->expectFailsRule(new PossibleFragmentSpreads, '
       fragment invalidUnionWithinInterface on Pet { ...humanOrAlienFragment }
@@ -221,7 +221,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('union into non overlapping union')
      */
-    public function testUnionIntoNonOverlappingUnion()
+    public function testUnionIntoNonOverlappingUnion() : void
     {
         $this->expectFailsRule(new PossibleFragmentSpreads, '
       fragment invalidUnionWithinUnion on CatOrDog { ...humanOrAlienFragment }
@@ -234,7 +234,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('interface into non implementing object')
      */
-    public function testInterfaceIntoNonImplementingObject()
+    public function testInterfaceIntoNonImplementingObject() : void
     {
         $this->expectFailsRule(new PossibleFragmentSpreads, '
       fragment invalidInterfaceWithinObject on Cat { ...intelligentFragment }
@@ -247,7 +247,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('interface into non overlapping interface')
      */
-    public function testInterfaceIntoNonOverlappingInterface()
+    public function testInterfaceIntoNonOverlappingInterface() : void
     {
         // Ideally this should fail, but our new lazy schema doesn't scan through all types and fields
         // So we don't have enough knowledge to check interface intersection and always allow this to pass:
@@ -263,7 +263,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('interface into non overlapping interface in inline fragment')
      */
-    public function testInterfaceIntoNonOverlappingInterfaceInInlineFragment()
+    public function testInterfaceIntoNonOverlappingInterfaceInInlineFragment() : void
     {
         // Ideally this should fail, but our new lazy schema doesn't scan through all types and fields
         // So we don't have enough knowledge to check interface intersection and always allow this to pass:
@@ -278,7 +278,7 @@ class PossibleFragmentSpreadsTest extends ValidatorTestCase
     /**
      * @see it('interface into non overlapping union')
      */
-    public function testInterfaceIntoNonOverlappingUnion()
+    public function testInterfaceIntoNonOverlappingUnion() : void
     {
         $this->expectFailsRule(new PossibleFragmentSpreads, '
       fragment invalidInterfaceWithinUnion on HumanOrAlien { ...petFragment }
diff --git a/tests/Validator/ProvidedNonNullArgumentsTest.php b/tests/Validator/ProvidedNonNullArgumentsTest.php
index a68ba97..25291e7 100644
--- a/tests/Validator/ProvidedNonNullArgumentsTest.php
+++ b/tests/Validator/ProvidedNonNullArgumentsTest.php
@@ -12,7 +12,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('ignores unknown arguments')
      */
-    public function testIgnoresUnknownArguments()
+    public function testIgnoresUnknownArguments() : void
     {
         // ignores unknown arguments
         $this->expectPassesRule(new ProvidedNonNullArguments, '
@@ -29,7 +29,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('Arg on optional arg')
      */
-    public function testArgOnOptionalArg()
+    public function testArgOnOptionalArg() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -43,7 +43,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('No Arg on optional arg')
      */
-    public function testNoArgOnOptionalArg()
+    public function testNoArgOnOptionalArg() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -57,7 +57,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('Multiple args')
      */
-    public function testMultipleArgs()
+    public function testMultipleArgs() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -71,7 +71,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('Multiple args reverse order')
      */
-    public function testMultipleArgsReverseOrder()
+    public function testMultipleArgsReverseOrder() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -85,7 +85,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('No args on multiple optional')
      */
-    public function testNoArgsOnMultipleOptional()
+    public function testNoArgsOnMultipleOptional() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -99,7 +99,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('One arg on multiple optional')
      */
-    public function testOneArgOnMultipleOptional()
+    public function testOneArgOnMultipleOptional() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -113,7 +113,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('Second arg on multiple optional')
      */
-    public function testSecondArgOnMultipleOptional()
+    public function testSecondArgOnMultipleOptional() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -127,7 +127,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('Multiple reqs on mixedList')
      */
-    public function testMultipleReqsOnMixedList()
+    public function testMultipleReqsOnMixedList() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -141,7 +141,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('Multiple reqs and one opt on mixedList')
      */
-    public function testMultipleReqsAndOneOptOnMixedList()
+    public function testMultipleReqsAndOneOptOnMixedList() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -155,7 +155,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('All reqs and opts on mixedList')
      */
-    public function testAllReqsAndOptsOnMixedList()
+    public function testAllReqsAndOptsOnMixedList() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -171,7 +171,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('Missing one non-nullable argument')
      */
-    public function testMissingOneNonNullableArgument()
+    public function testMissingOneNonNullableArgument() : void
     {
         $this->expectFailsRule(new ProvidedNonNullArguments, '
         {
@@ -187,7 +187,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('Missing multiple non-nullable arguments')
      */
-    public function testMissingMultipleNonNullableArguments()
+    public function testMissingMultipleNonNullableArguments() : void
     {
         $this->expectFailsRule(new ProvidedNonNullArguments, '
         {
@@ -204,7 +204,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('Incorrect value and missing argument')
      */
-    public function testIncorrectValueAndMissingArgument()
+    public function testIncorrectValueAndMissingArgument() : void
     {
         $this->expectFailsRule(new ProvidedNonNullArguments, '
         {
@@ -222,7 +222,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('ignores unknown directives')
      */
-    public function testIgnoresUnknownDirectives()
+    public function testIgnoresUnknownDirectives() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -234,7 +234,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('with directives of valid types')
      */
-    public function testWithDirectivesOfValidTypes()
+    public function testWithDirectivesOfValidTypes() : void
     {
         $this->expectPassesRule(new ProvidedNonNullArguments, '
         {
@@ -251,7 +251,7 @@ class ProvidedNonNullArgumentsTest extends ValidatorTestCase
     /**
      * @see it('with directive with missing types')
      */
-    public function testWithDirectiveWithMissingTypes()
+    public function testWithDirectiveWithMissingTypes() : void
     {
         $this->expectFailsRule(new ProvidedNonNullArguments, '
         {
diff --git a/tests/Validator/QueryComplexityTest.php b/tests/Validator/QueryComplexityTest.php
index ed6d74f..dcc1852 100644
--- a/tests/Validator/QueryComplexityTest.php
+++ b/tests/Validator/QueryComplexityTest.php
@@ -41,49 +41,49 @@ class QueryComplexityTest extends QuerySecurityTestCase
         return self::$rule;
     }
 
-    public function testSimpleQueries()
+    public function testSimpleQueries() : void
     {
         $query = 'query MyQuery { human { firstName } }';
 
         $this->assertDocumentValidators($query, 2, 3);
     }
 
-    public function testInlineFragmentQueries()
+    public function testInlineFragmentQueries() : void
     {
         $query = 'query MyQuery { human { ... on Human { firstName } } }';
 
         $this->assertDocumentValidators($query, 2, 3);
     }
 
-    public function testFragmentQueries()
+    public function testFragmentQueries() : void
     {
         $query = 'query MyQuery { human { ...F1 } } fragment F1 on Human { firstName}';
 
         $this->assertDocumentValidators($query, 2, 3);
     }
 
-    public function testAliasesQueries()
+    public function testAliasesQueries() : void
     {
         $query = 'query MyQuery { thomas: human(name: "Thomas") { firstName } jeremy: human(name: "Jeremy") { firstName } }';
 
         $this->assertDocumentValidators($query, 4, 5);
     }
 
-    public function testCustomComplexityQueries()
+    public function testCustomComplexityQueries() : void
     {
         $query = 'query MyQuery { human { dogs { name } } }';
 
         $this->assertDocumentValidators($query, 12, 13);
     }
 
-    public function testCustomComplexityWithArgsQueries()
+    public function testCustomComplexityWithArgsQueries() : void
     {
         $query = 'query MyQuery { human { dogs(name: "Root") { name } } }';
 
         $this->assertDocumentValidators($query, 3, 4);
     }
 
-    public function testCustomComplexityWithVariablesQueries()
+    public function testCustomComplexityWithVariablesQueries() : void
     {
         $query = 'query MyQuery($dog: String!) { human { dogs(name: $dog) { name } } }';
 
@@ -92,7 +92,7 @@ class QueryComplexityTest extends QuerySecurityTestCase
         $this->assertDocumentValidators($query, 3, 4);
     }
 
-    public function testQueryWithEnabledIncludeDirectives()
+    public function testQueryWithEnabledIncludeDirectives() : void
     {
         $query = 'query MyQuery($withDogs: Boolean!) { human { dogs(name: "Root") @include(if:$withDogs) { name } } }';
 
@@ -101,7 +101,7 @@ class QueryComplexityTest extends QuerySecurityTestCase
         $this->assertDocumentValidators($query, 3, 4);
     }
 
-    public function testQueryWithDisabledIncludeDirectives()
+    public function testQueryWithDisabledIncludeDirectives() : void
     {
         $query = 'query MyQuery($withDogs: Boolean!) { human { dogs(name: "Root") @include(if:$withDogs) { name } } }';
 
@@ -110,7 +110,7 @@ class QueryComplexityTest extends QuerySecurityTestCase
         $this->assertDocumentValidators($query, 1, 2);
     }
 
-    public function testQueryWithEnabledSkipDirectives()
+    public function testQueryWithEnabledSkipDirectives() : void
     {
         $query = 'query MyQuery($withoutDogs: Boolean!) { human { dogs(name: "Root") @skip(if:$withoutDogs) { name } } }';
 
@@ -119,7 +119,7 @@ class QueryComplexityTest extends QuerySecurityTestCase
         $this->assertDocumentValidators($query, 1, 2);
     }
 
-    public function testQueryWithDisabledSkipDirectives()
+    public function testQueryWithDisabledSkipDirectives() : void
     {
         $query = 'query MyQuery($withoutDogs: Boolean!) { human { dogs(name: "Root") @skip(if:$withoutDogs) { name } } }';
 
@@ -128,7 +128,7 @@ class QueryComplexityTest extends QuerySecurityTestCase
         $this->assertDocumentValidators($query, 3, 4);
     }
 
-    public function testQueryWithMultipleDirectives()
+    public function testQueryWithMultipleDirectives() : void
     {
         $query = 'query MyQuery($withDogs: Boolean!, $withoutDogName: Boolean!) { human { dogs(name: "Root") @include(if:$withDogs) { name @skip(if:$withoutDogName) } } }';
 
@@ -140,22 +140,22 @@ class QueryComplexityTest extends QuerySecurityTestCase
         $this->assertDocumentValidators($query, 2, 3);
     }
 
-    public function testComplexityIntrospectionQuery()
+    public function testComplexityIntrospectionQuery() : void
     {
         $this->assertIntrospectionQuery(181);
     }
 
-    public function testIntrospectionTypeMetaFieldQuery()
+    public function testIntrospectionTypeMetaFieldQuery() : void
     {
         $this->assertIntrospectionTypeMetaFieldQuery(2);
     }
 
-    public function testTypeNameMetaFieldQuery()
+    public function testTypeNameMetaFieldQuery() : void
     {
         $this->assertTypeNameMetaFieldQuery(3);
     }
 
-    public function testSkippedWhenThereAreOtherValidationErrors()
+    public function testSkippedWhenThereAreOtherValidationErrors() : void
     {
         $query = 'query MyQuery { human(name: INVALID_VALUE) { dogs {name} } }';
 
diff --git a/tests/Validator/QueryDepthTest.php b/tests/Validator/QueryDepthTest.php
index 5f63936..1063156 100644
--- a/tests/Validator/QueryDepthTest.php
+++ b/tests/Validator/QueryDepthTest.php
@@ -32,7 +32,7 @@ class QueryDepthTest extends QuerySecurityTestCase
      * @param array $expectedErrors
      * @dataProvider queryDataProvider
      */
-    public function testSimpleQueries($queryDepth, $maxQueryDepth = 7, $expectedErrors = [])
+    public function testSimpleQueries($queryDepth, $maxQueryDepth = 7, $expectedErrors = []) : void
     {
         $this->assertDocumentValidator($this->buildRecursiveQuery($queryDepth), $maxQueryDepth, $expectedErrors);
     }
@@ -43,7 +43,7 @@ class QueryDepthTest extends QuerySecurityTestCase
      * @param array $expectedErrors
      * @dataProvider queryDataProvider
      */
-    public function testFragmentQueries($queryDepth, $maxQueryDepth = 7, $expectedErrors = [])
+    public function testFragmentQueries($queryDepth, $maxQueryDepth = 7, $expectedErrors = []) : void
     {
         $this->assertDocumentValidator($this->buildRecursiveUsingFragmentQuery($queryDepth), $maxQueryDepth, $expectedErrors);
     }
@@ -54,22 +54,22 @@ class QueryDepthTest extends QuerySecurityTestCase
      * @param array $expectedErrors
      * @dataProvider queryDataProvider
      */
-    public function testInlineFragmentQueries($queryDepth, $maxQueryDepth = 7, $expectedErrors = [])
+    public function testInlineFragmentQueries($queryDepth, $maxQueryDepth = 7, $expectedErrors = []) : void
     {
         $this->assertDocumentValidator($this->buildRecursiveUsingInlineFragmentQuery($queryDepth), $maxQueryDepth, $expectedErrors);
     }
 
-    public function testComplexityIntrospectionQuery()
+    public function testComplexityIntrospectionQuery() : void
     {
         $this->assertIntrospectionQuery(11);
     }
 
-    public function testIntrospectionTypeMetaFieldQuery()
+    public function testIntrospectionTypeMetaFieldQuery() : void
     {
         $this->assertIntrospectionTypeMetaFieldQuery(1);
     }
 
-    public function testTypeNameMetaFieldQuery()
+    public function testTypeNameMetaFieldQuery() : void
     {
         $this->assertTypeNameMetaFieldQuery(1);
     }
diff --git a/tests/Validator/QuerySecurityTestCase.php b/tests/Validator/QuerySecurityTestCase.php
index 9bb07aa..5188e3e 100644
--- a/tests/Validator/QuerySecurityTestCase.php
+++ b/tests/Validator/QuerySecurityTestCase.php
@@ -29,7 +29,7 @@ abstract class QuerySecurityTestCase extends TestCase
      * @expectedException \InvalidArgumentException
      * @expectedExceptionMessage argument must be greater or equal to 0.
      */
-    public function testMaxQueryDepthMustBeGreaterOrEqualTo0()
+    public function testMaxQueryDepthMustBeGreaterOrEqualTo0() : void
     {
         $this->getRule(-1);
     }
diff --git a/tests/Validator/ScalarLeafsTest.php b/tests/Validator/ScalarLeafsTest.php
index 2027295..1d9db96 100644
--- a/tests/Validator/ScalarLeafsTest.php
+++ b/tests/Validator/ScalarLeafsTest.php
@@ -12,7 +12,7 @@ class ScalarLeafsTest extends ValidatorTestCase
     /**
      * @see it('valid scalar selection')
      */
-    public function testValidScalarSelection()
+    public function testValidScalarSelection() : void
     {
         $this->expectPassesRule(new ScalarLeafs, '
       fragment scalarSelection on Dog {
@@ -24,7 +24,7 @@ class ScalarLeafsTest extends ValidatorTestCase
     /**
      * @see it('object type missing selection')
      */
-    public function testObjectTypeMissingSelection()
+    public function testObjectTypeMissingSelection() : void
     {
         $this->expectFailsRule(new ScalarLeafs, '
       query directQueryOnObjectWithoutSubFields {
@@ -36,7 +36,7 @@ class ScalarLeafsTest extends ValidatorTestCase
     /**
      * @see it('interface type missing selection')
      */
-    public function testInterfaceTypeMissingSelection()
+    public function testInterfaceTypeMissingSelection() : void
     {
         $this->expectFailsRule(new ScalarLeafs, '
       {
@@ -48,7 +48,7 @@ class ScalarLeafsTest extends ValidatorTestCase
     /**
      * @see it('valid scalar selection with args')
      */
-    public function testValidScalarSelectionWithArgs()
+    public function testValidScalarSelectionWithArgs() : void
     {
         $this->expectPassesRule(new ScalarLeafs, '
       fragment scalarSelectionWithArgs on Dog {
@@ -60,7 +60,7 @@ class ScalarLeafsTest extends ValidatorTestCase
     /**
      * @see it('scalar selection not allowed on Boolean')
      */
-    public function testScalarSelectionNotAllowedOnBoolean()
+    public function testScalarSelectionNotAllowedOnBoolean() : void
     {
         $this->expectFailsRule(new ScalarLeafs, '
       fragment scalarSelectionsNotAllowedOnBoolean on Dog {
@@ -73,7 +73,7 @@ class ScalarLeafsTest extends ValidatorTestCase
     /**
      * @see it('scalar selection not allowed on Enum')
      */
-    public function testScalarSelectionNotAllowedOnEnum()
+    public function testScalarSelectionNotAllowedOnEnum() : void
     {
         $this->expectFailsRule(new ScalarLeafs, '
       fragment scalarSelectionsNotAllowedOnEnum on Cat {
@@ -87,7 +87,7 @@ class ScalarLeafsTest extends ValidatorTestCase
     /**
      * @see it('scalar selection not allowed with args')
      */
-    public function testScalarSelectionNotAllowedWithArgs()
+    public function testScalarSelectionNotAllowedWithArgs() : void
     {
         $this->expectFailsRule(new ScalarLeafs, '
       fragment scalarSelectionsNotAllowedWithArgs on Dog {
@@ -101,7 +101,7 @@ class ScalarLeafsTest extends ValidatorTestCase
     /**
      * @see it('Scalar selection not allowed with directives')
      */
-    public function testScalarSelectionNotAllowedWithDirectives()
+    public function testScalarSelectionNotAllowedWithDirectives() : void
     {
         $this->expectFailsRule(new ScalarLeafs, '
       fragment scalarSelectionsNotAllowedWithDirectives on Dog {
@@ -115,7 +115,7 @@ class ScalarLeafsTest extends ValidatorTestCase
     /**
      * @see it('Scalar selection not allowed with directives and args')
      */
-    public function testScalarSelectionNotAllowedWithDirectivesAndArgs()
+    public function testScalarSelectionNotAllowedWithDirectivesAndArgs() : void
     {
         $this->expectFailsRule(new ScalarLeafs, '
       fragment scalarSelectionsNotAllowedWithDirectivesAndArgs on Dog {
diff --git a/tests/Validator/UniqueArgumentNamesTest.php b/tests/Validator/UniqueArgumentNamesTest.php
index 8df6840..4652aa1 100644
--- a/tests/Validator/UniqueArgumentNamesTest.php
+++ b/tests/Validator/UniqueArgumentNamesTest.php
@@ -12,7 +12,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('no arguments on field')
      */
-    public function testNoArgumentsOnField()
+    public function testNoArgumentsOnField() : void
     {
         $this->expectPassesRule(new UniqueArgumentNames(), '
       {
@@ -24,7 +24,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('no arguments on directive')
      */
-    public function testNoArgumentsOnDirective()
+    public function testNoArgumentsOnDirective() : void
     {
         $this->expectPassesRule(new UniqueArgumentNames, '
       {
@@ -36,7 +36,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('argument on field')
      */
-    public function testArgumentOnField()
+    public function testArgumentOnField() : void
     {
         $this->expectPassesRule(new UniqueArgumentNames, '
       {
@@ -48,7 +48,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('argument on directive')
      */
-    public function testArgumentOnDirective()
+    public function testArgumentOnDirective() : void
     {
         $this->expectPassesRule(new UniqueArgumentNames, '
       {
@@ -60,7 +60,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('same argument on two fields')
      */
-    public function testSameArgumentOnTwoFields()
+    public function testSameArgumentOnTwoFields() : void
     {
         $this->expectPassesRule(new UniqueArgumentNames, '
       {
@@ -73,7 +73,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('same argument on field and directive')
      */
-    public function testSameArgumentOnFieldAndDirective()
+    public function testSameArgumentOnFieldAndDirective() : void
     {
         $this->expectPassesRule(new UniqueArgumentNames, '
       {
@@ -85,7 +85,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('same argument on two directives')
      */
-    public function testSameArgumentOnTwoDirectives()
+    public function testSameArgumentOnTwoDirectives() : void
     {
         $this->expectPassesRule(new UniqueArgumentNames, '
       {
@@ -97,7 +97,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple field arguments')
      */
-    public function testMultipleFieldArguments()
+    public function testMultipleFieldArguments() : void
     {
         $this->expectPassesRule(new UniqueArgumentNames, '
       {
@@ -109,7 +109,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple directive arguments')
      */
-    public function testMultipleDirectiveArguments()
+    public function testMultipleDirectiveArguments() : void
     {
         $this->expectPassesRule(new UniqueArgumentNames, '
       {
@@ -121,7 +121,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('duplicate field arguments')
      */
-    public function testDuplicateFieldArguments()
+    public function testDuplicateFieldArguments() : void
     {
         $this->expectFailsRule(new UniqueArgumentNames, '
       {
@@ -135,7 +135,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('many duplicate field arguments')
      */
-    public function testManyDuplicateFieldArguments()
+    public function testManyDuplicateFieldArguments() : void
     {
         $this->expectFailsRule(new UniqueArgumentNames, '
       {
@@ -150,7 +150,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('duplicate directive arguments')
      */
-    public function testDuplicateDirectiveArguments()
+    public function testDuplicateDirectiveArguments() : void
     {
         $this->expectFailsRule(new UniqueArgumentNames, '
       {
@@ -164,7 +164,7 @@ class UniqueArgumentNamesTest extends ValidatorTestCase
     /**
      * @see it('many duplicate directive arguments')
      */
-    public function testManyDuplicateDirectiveArguments()
+    public function testManyDuplicateDirectiveArguments() : void
     {
         $this->expectFailsRule(new UniqueArgumentNames, '
       {
diff --git a/tests/Validator/UniqueDirectivesPerLocationTest.php b/tests/Validator/UniqueDirectivesPerLocationTest.php
index c08f55d..199f106 100644
--- a/tests/Validator/UniqueDirectivesPerLocationTest.php
+++ b/tests/Validator/UniqueDirectivesPerLocationTest.php
@@ -8,7 +8,7 @@ class UniqueDirectivesPerLocationTest extends ValidatorTestCase
     /**
      * @see it('no directives')
      */
-    public function testNoDirectives()
+    public function testNoDirectives() : void
     {
         $this->expectPassesRule(new UniqueDirectivesPerLocation(), '
       fragment Test on Type {
@@ -20,7 +20,7 @@ class UniqueDirectivesPerLocationTest extends ValidatorTestCase
     /**
      * @see it('unique directives in different locations')
      */
-    public function testUniqueDirectivesInDifferentLocations()
+    public function testUniqueDirectivesInDifferentLocations() : void
     {
         $this->expectPassesRule(new UniqueDirectivesPerLocation(), '
       fragment Test on Type @directiveA {
@@ -32,7 +32,7 @@ class UniqueDirectivesPerLocationTest extends ValidatorTestCase
     /**
      * @see it('unique directives in same locations')
      */
-    public function testUniqueDirectivesInSameLocations()
+    public function testUniqueDirectivesInSameLocations() : void
     {
         $this->expectPassesRule(new UniqueDirectivesPerLocation(), '
       fragment Test on Type @directiveA @directiveB {
@@ -44,7 +44,7 @@ class UniqueDirectivesPerLocationTest extends ValidatorTestCase
     /**
      * @see it('same directives in different locations')
      */
-    public function testSameDirectivesInDifferentLocations()
+    public function testSameDirectivesInDifferentLocations() : void
     {
         $this->expectPassesRule(new UniqueDirectivesPerLocation(), '
       fragment Test on Type @directiveA {
@@ -56,7 +56,7 @@ class UniqueDirectivesPerLocationTest extends ValidatorTestCase
     /**
      * @see it('same directives in similar locations')
      */
-    public function testSameDirectivesInSimilarLocations()
+    public function testSameDirectivesInSimilarLocations() : void
     {
         $this->expectPassesRule(new UniqueDirectivesPerLocation(), '
       fragment Test on Type {
@@ -69,7 +69,7 @@ class UniqueDirectivesPerLocationTest extends ValidatorTestCase
     /**
      * @see it('duplicate directives in one location')
      */
-    public function testDuplicateDirectivesInOneLocation()
+    public function testDuplicateDirectivesInOneLocation() : void
     {
         $this->expectFailsRule(new UniqueDirectivesPerLocation(), '
       fragment Test on Type {
@@ -83,7 +83,7 @@ class UniqueDirectivesPerLocationTest extends ValidatorTestCase
     /**
      * @see it('many duplicate directives in one location')
      */
-    public function testManyDuplicateDirectivesInOneLocation()
+    public function testManyDuplicateDirectivesInOneLocation() : void
     {
         $this->expectFailsRule(new UniqueDirectivesPerLocation(), '
       fragment Test on Type {
@@ -98,7 +98,7 @@ class UniqueDirectivesPerLocationTest extends ValidatorTestCase
     /**
      * @see it('different duplicate directives in one location')
      */
-    public function testDifferentDuplicateDirectivesInOneLocation()
+    public function testDifferentDuplicateDirectivesInOneLocation() : void
     {
         $this->expectFailsRule(new UniqueDirectivesPerLocation, '
       fragment Test on Type {
@@ -113,7 +113,7 @@ class UniqueDirectivesPerLocationTest extends ValidatorTestCase
     /**
      * @see it('duplicate directives in many locations')
      */
-    public function testDuplicateDirectivesInManyLocations()
+    public function testDuplicateDirectivesInManyLocations() : void
     {
         $this->expectFailsRule(new UniqueDirectivesPerLocation(), '
       fragment Test on Type @directive @directive {
diff --git a/tests/Validator/UniqueFragmentNamesTest.php b/tests/Validator/UniqueFragmentNamesTest.php
index d3923e9..426e803 100644
--- a/tests/Validator/UniqueFragmentNamesTest.php
+++ b/tests/Validator/UniqueFragmentNamesTest.php
@@ -12,7 +12,7 @@ class UniqueFragmentNamesTest extends ValidatorTestCase
     /**
      * @see it('no fragments')
      */
-    public function testNoFragments()
+    public function testNoFragments() : void
     {
         $this->expectPassesRule(new UniqueFragmentNames(), '
       {
@@ -24,7 +24,7 @@ class UniqueFragmentNamesTest extends ValidatorTestCase
     /**
      * @see it('one fragment')
      */
-    public function testOneFragment()
+    public function testOneFragment() : void
     {
         $this->expectPassesRule(new UniqueFragmentNames, '
       {
@@ -40,7 +40,7 @@ class UniqueFragmentNamesTest extends ValidatorTestCase
     /**
      * @see it('many fragments')
      */
-    public function testManyFragments()
+    public function testManyFragments() : void
     {
         $this->expectPassesRule(new UniqueFragmentNames, '
       {
@@ -63,7 +63,7 @@ class UniqueFragmentNamesTest extends ValidatorTestCase
     /**
      * @see it('inline fragments are always unique')
      */
-    public function testInlineFragmentsAreAlwaysUnique()
+    public function testInlineFragmentsAreAlwaysUnique() : void
     {
         $this->expectPassesRule(new UniqueFragmentNames, '
       {
@@ -80,7 +80,7 @@ class UniqueFragmentNamesTest extends ValidatorTestCase
     /**
      * @see it('fragment and operation named the same')
      */
-    public function testFragmentAndOperationNamedTheSame()
+    public function testFragmentAndOperationNamedTheSame() : void
     {
         $this->expectPassesRule(new UniqueFragmentNames, '
       query Foo {
@@ -95,7 +95,7 @@ class UniqueFragmentNamesTest extends ValidatorTestCase
     /**
      * @see it('fragments named the same')
      */
-    public function testFragmentsNamedTheSame()
+    public function testFragmentsNamedTheSame() : void
     {
         $this->expectFailsRule(new UniqueFragmentNames, '
       {
@@ -115,7 +115,7 @@ class UniqueFragmentNamesTest extends ValidatorTestCase
     /**
      * @see it('fragments named the same without being referenced')
      */
-    public function testFragmentsNamedTheSameWithoutBeingReferenced()
+    public function testFragmentsNamedTheSameWithoutBeingReferenced() : void
     {
         $this->expectFailsRule(new UniqueFragmentNames, '
       fragment fragA on Type {
diff --git a/tests/Validator/UniqueInputFieldNamesTest.php b/tests/Validator/UniqueInputFieldNamesTest.php
index 4ac48b2..676dea3 100644
--- a/tests/Validator/UniqueInputFieldNamesTest.php
+++ b/tests/Validator/UniqueInputFieldNamesTest.php
@@ -12,7 +12,7 @@ class UniqueInputFieldNamesTest extends ValidatorTestCase
     /**
      * @see it('input object with fields')
      */
-    public function testInputObjectWithFields()
+    public function testInputObjectWithFields() : void
     {
         $this->expectPassesRule(new UniqueInputFieldNames(), '
       {
@@ -24,7 +24,7 @@ class UniqueInputFieldNamesTest extends ValidatorTestCase
     /**
      * @see it('same input object within two args')
      */
-    public function testSameInputObjectWithinTwoArgs()
+    public function testSameInputObjectWithinTwoArgs() : void
     {
         $this->expectPassesRule(new UniqueInputFieldNames, '
       {
@@ -36,7 +36,7 @@ class UniqueInputFieldNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple input object fields')
      */
-    public function testMultipleInputObjectFields()
+    public function testMultipleInputObjectFields() : void
     {
         $this->expectPassesRule(new UniqueInputFieldNames, '
       {
@@ -48,7 +48,7 @@ class UniqueInputFieldNamesTest extends ValidatorTestCase
     /**
      * @see it('allows for nested input objects with similar fields')
      */
-    public function testAllowsForNestedInputObjectsWithSimilarFields()
+    public function testAllowsForNestedInputObjectsWithSimilarFields() : void
     {
         $this->expectPassesRule(new UniqueInputFieldNames, '
       {
@@ -68,7 +68,7 @@ class UniqueInputFieldNamesTest extends ValidatorTestCase
     /**
      * @see it('duplicate input object fields')
      */
-    public function testDuplicateInputObjectFields()
+    public function testDuplicateInputObjectFields() : void
     {
         $this->expectFailsRule(new UniqueInputFieldNames, '
       {
@@ -82,7 +82,7 @@ class UniqueInputFieldNamesTest extends ValidatorTestCase
     /**
      * @see it('many duplicate input object fields')
      */
-    public function testManyDuplicateInputObjectFields()
+    public function testManyDuplicateInputObjectFields() : void
     {
         $this->expectFailsRule(new UniqueInputFieldNames, '
       {
diff --git a/tests/Validator/UniqueOperationNamesTest.php b/tests/Validator/UniqueOperationNamesTest.php
index f0a9f02..11cecdc 100644
--- a/tests/Validator/UniqueOperationNamesTest.php
+++ b/tests/Validator/UniqueOperationNamesTest.php
@@ -12,7 +12,7 @@ class UniqueOperationNamesTest extends ValidatorTestCase
     /**
      * @see it('no operations')
      */
-    public function testNoOperations()
+    public function testNoOperations() : void
     {
         $this->expectPassesRule(new UniqueOperationNames(), '
       fragment fragA on Type {
@@ -24,7 +24,7 @@ class UniqueOperationNamesTest extends ValidatorTestCase
     /**
      * @see it('one anon operation')
      */
-    public function testOneAnonOperation()
+    public function testOneAnonOperation() : void
     {
         $this->expectPassesRule(new UniqueOperationNames, '
       {
@@ -36,7 +36,7 @@ class UniqueOperationNamesTest extends ValidatorTestCase
     /**
      * @see it('one named operation')
      */
-    public function testOneNamedOperation()
+    public function testOneNamedOperation() : void
     {
         $this->expectPassesRule(new UniqueOperationNames, '
       query Foo {
@@ -48,7 +48,7 @@ class UniqueOperationNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple operations')
      */
-    public function testMultipleOperations()
+    public function testMultipleOperations() : void
     {
         $this->expectPassesRule(new UniqueOperationNames, '
       query Foo {
@@ -64,7 +64,7 @@ class UniqueOperationNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple operations of different types')
      */
-    public function testMultipleOperationsOfDifferentTypes()
+    public function testMultipleOperationsOfDifferentTypes() : void
     {
         $this->expectPassesRule(new UniqueOperationNames, '
       query Foo {
@@ -84,7 +84,7 @@ class UniqueOperationNamesTest extends ValidatorTestCase
     /**
      * @see it('fragment and operation named the same')
      */
-    public function testFragmentAndOperationNamedTheSame()
+    public function testFragmentAndOperationNamedTheSame() : void
     {
         $this->expectPassesRule(new UniqueOperationNames, '
       query Foo {
@@ -99,7 +99,7 @@ class UniqueOperationNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple operations of same name')
      */
-    public function testMultipleOperationsOfSameName()
+    public function testMultipleOperationsOfSameName() : void
     {
         $this->expectFailsRule(new UniqueOperationNames, '
       query Foo {
@@ -116,7 +116,7 @@ class UniqueOperationNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple ops of same name of different types (mutation)')
      */
-    public function testMultipleOpsOfSameNameOfDifferentTypes_Mutation()
+    public function testMultipleOpsOfSameNameOfDifferentTypesMutation() : void
     {
         $this->expectFailsRule(new UniqueOperationNames, '
       query Foo {
@@ -133,7 +133,7 @@ class UniqueOperationNamesTest extends ValidatorTestCase
     /**
      * @see it('multiple ops of same name of different types (subscription)')
      */
-    public function testMultipleOpsOfSameNameOfDifferentTypes_Subscription()
+    public function testMultipleOpsOfSameNameOfDifferentTypesSubscription() : void
     {
         $this->expectFailsRule(new UniqueOperationNames, '
       query Foo {
diff --git a/tests/Validator/UniqueVariableNamesTest.php b/tests/Validator/UniqueVariableNamesTest.php
index 2b93a91..a5776a4 100644
--- a/tests/Validator/UniqueVariableNamesTest.php
+++ b/tests/Validator/UniqueVariableNamesTest.php
@@ -12,7 +12,7 @@ class UniqueVariableNamesTest extends ValidatorTestCase
     /**
      * @see it('unique variable names')
      */
-    public function testUniqueVariableNames()
+    public function testUniqueVariableNames() : void
     {
         $this->expectPassesRule(new UniqueVariableNames(), '
       query A($x: Int, $y: String) { __typename }
@@ -23,7 +23,7 @@ class UniqueVariableNamesTest extends ValidatorTestCase
     /**
      * @see it('duplicate variable names')
      */
-    public function testDuplicateVariableNames()
+    public function testDuplicateVariableNames() : void
     {
         $this->expectFailsRule(new UniqueVariableNames, '
       query A($x: Int, $x: Int, $x: String) { __typename }
diff --git a/tests/Validator/ValidationTest.php b/tests/Validator/ValidationTest.php
index 6d008f7..7bfb4b2 100644
--- a/tests/Validator/ValidationTest.php
+++ b/tests/Validator/ValidationTest.php
@@ -8,7 +8,7 @@ class ValidationTest extends ValidatorTestCase
     /**
      * @see it('validates queries')
      */
-    public function testValidatesQueries()
+    public function testValidatesQueries() : void
     {
         $this->expectPassesCompleteValidation('
           query {
@@ -27,7 +27,7 @@ class ValidationTest extends ValidatorTestCase
     /**
      * @see it('detects bad scalar parse')
      */
-    public function testDetectsBadScalarParse()
+    public function testDetectsBadScalarParse() : void
     {
         $doc = '
       query {
@@ -48,7 +48,7 @@ class ValidationTest extends ValidatorTestCase
         );
     }
 
-    public function testPassesValidationWithEmptyRules()
+    public function testPassesValidationWithEmptyRules() : void
     {
         $query = '{invalid}';
 
diff --git a/tests/Validator/ValuesOfCorrectTypeTest.php b/tests/Validator/ValuesOfCorrectTypeTest.php
index 3bf4bb2..2d9f79b 100644
--- a/tests/Validator/ValuesOfCorrectTypeTest.php
+++ b/tests/Validator/ValuesOfCorrectTypeTest.php
@@ -47,7 +47,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Good int value')
      */
-    public function testGoodIntValue()
+    public function testGoodIntValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -61,7 +61,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Good negative int value')
      */
-    public function testGoodNegativeIntValue()
+    public function testGoodNegativeIntValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -75,7 +75,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Good boolean value')
      */
-    public function testGoodBooleanValue()
+    public function testGoodBooleanValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -89,7 +89,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Good string value')
      */
-    public function testGoodStringValue()
+    public function testGoodStringValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -103,7 +103,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Good float value')
      */
-    public function testGoodFloatValue()
+    public function testGoodFloatValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -114,7 +114,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
         ');
     }
 
-    public function testGoodNegativeFloatValue()
+    public function testGoodNegativeFloatValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -128,7 +128,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Int into Float')
      */
-    public function testIntIntoFloat()
+    public function testIntIntoFloat() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -142,7 +142,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Int into ID')
      */
-    public function testIntIntoID()
+    public function testIntIntoID() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -156,7 +156,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('String into ID')
      */
-    public function testStringIntoID()
+    public function testStringIntoID() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -170,7 +170,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Good enum value')
      */
-    public function testGoodEnumValue()
+    public function testGoodEnumValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -184,7 +184,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Enum with null value')
      */
-    public function testEnumWithNullValue()
+    public function testEnumWithNullValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -198,7 +198,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('null into nullable type')
      */
-    public function testNullIntoNullableType()
+    public function testNullIntoNullableType() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -222,7 +222,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Int into String')
      */
-    public function testIntIntoString()
+    public function testIntIntoString() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -238,7 +238,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Float into String')
      */
-    public function testFloatIntoString()
+    public function testFloatIntoString() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -254,7 +254,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Boolean into String')
      */
-    public function testBooleanIntoString()
+    public function testBooleanIntoString() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -270,7 +270,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Unquoted String into String')
      */
-    public function testUnquotedStringIntoString()
+    public function testUnquotedStringIntoString() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -288,7 +288,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('String into Int')
      */
-    public function testStringIntoInt()
+    public function testStringIntoInt() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -304,7 +304,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Big Int into Int')
      */
-    public function testBigIntIntoInt()
+    public function testBigIntIntoInt() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -320,7 +320,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Unquoted String into Int')
      */
-    public function testUnquotedStringIntoInt()
+    public function testUnquotedStringIntoInt() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -336,7 +336,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Simple Float into Int')
      */
-    public function testSimpleFloatIntoInt()
+    public function testSimpleFloatIntoInt() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -352,7 +352,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Float into Int')
      */
-    public function testFloatIntoInt()
+    public function testFloatIntoInt() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -370,7 +370,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('String into Float')
      */
-    public function testStringIntoFloat()
+    public function testStringIntoFloat() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -386,7 +386,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Boolean into Float')
      */
-    public function testBooleanIntoFloat()
+    public function testBooleanIntoFloat() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -402,7 +402,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Unquoted into Float')
      */
-    public function testUnquotedIntoFloat()
+    public function testUnquotedIntoFloat() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -420,7 +420,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Int into Boolean')
      */
-    public function testIntIntoBoolean()
+    public function testIntIntoBoolean() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -436,7 +436,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Float into Boolean')
      */
-    public function testFloatIntoBoolean()
+    public function testFloatIntoBoolean() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -452,7 +452,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('String into Boolean')
      */
-    public function testStringIntoBoolean()
+    public function testStringIntoBoolean() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -468,7 +468,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Unquoted into Boolean')
      */
-    public function testUnquotedIntoBoolean()
+    public function testUnquotedIntoBoolean() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -486,7 +486,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Float into ID')
      */
-    public function testFloatIntoID()
+    public function testFloatIntoID() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -502,7 +502,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Boolean into ID')
      */
-    public function testBooleanIntoID()
+    public function testBooleanIntoID() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -518,7 +518,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Unquoted into ID')
      */
-    public function testUnquotedIntoID()
+    public function testUnquotedIntoID() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -536,7 +536,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Int into Enum')
      */
-    public function testIntIntoEnum()
+    public function testIntIntoEnum() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -552,7 +552,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Float into Enum')
      */
-    public function testFloatIntoEnum()
+    public function testFloatIntoEnum() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -568,7 +568,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('String into Enum')
      */
-    public function testStringIntoEnum()
+    public function testStringIntoEnum() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -590,7 +590,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Boolean into Enum')
      */
-    public function testBooleanIntoEnum()
+    public function testBooleanIntoEnum() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -606,7 +606,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Unknown Enum Value into Enum')
      */
-    public function testUnknownEnumValueIntoEnum()
+    public function testUnknownEnumValueIntoEnum() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -622,7 +622,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Different case Enum Value into Enum')
      */
-    public function testDifferentCaseEnumValueIntoEnum()
+    public function testDifferentCaseEnumValueIntoEnum() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -646,7 +646,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Good list value')
      */
-    public function testGoodListValue()
+    public function testGoodListValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -660,7 +660,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Empty list value')
      */
-    public function testEmptyListValue()
+    public function testEmptyListValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -674,7 +674,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Null value')
      */
-    public function testNullValue()
+    public function testNullValue() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -688,7 +688,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Single value into List')
      */
-    public function testSingleValueIntoList()
+    public function testSingleValueIntoList() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -704,7 +704,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Incorrect item type')
      */
-    public function testIncorrectItemtype()
+    public function testIncorrectItemtype() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -720,7 +720,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Single value of incorrect type')
      */
-    public function testSingleValueOfIncorrectType()
+    public function testSingleValueOfIncorrectType() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -738,7 +738,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Arg on optional arg')
      */
-    public function testArgOnOptionalArg()
+    public function testArgOnOptionalArg() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -752,7 +752,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('No Arg on optional arg')
      */
-    public function testNoArgOnOptionalArg()
+    public function testNoArgOnOptionalArg() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -766,7 +766,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Multiple args')
      */
-    public function testMultipleArgs()
+    public function testMultipleArgs() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -780,7 +780,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Multiple args reverse order')
      */
-    public function testMultipleArgsReverseOrder()
+    public function testMultipleArgsReverseOrder() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -794,7 +794,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('No args on multiple optional')
      */
-    public function testNoArgsOnMultipleOptional()
+    public function testNoArgsOnMultipleOptional() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -808,7 +808,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('One arg on multiple optional')
      */
-    public function testOneArgOnMultipleOptional()
+    public function testOneArgOnMultipleOptional() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -822,7 +822,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Second arg on multiple optional')
      */
-    public function testSecondArgOnMultipleOptional()
+    public function testSecondArgOnMultipleOptional() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -836,7 +836,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Multiple reqs on mixedList')
      */
-    public function testMultipleReqsOnMixedList()
+    public function testMultipleReqsOnMixedList() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -850,7 +850,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Multiple reqs and one opt on mixedList')
      */
-    public function testMultipleReqsAndOneOptOnMixedList()
+    public function testMultipleReqsAndOneOptOnMixedList() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -864,7 +864,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('All reqs and opts on mixedList')
      */
-    public function testAllReqsAndOptsOnMixedList()
+    public function testAllReqsAndOptsOnMixedList() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -880,7 +880,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Incorrect value type')
      */
-    public function testIncorrectValueType()
+    public function testIncorrectValueType() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -897,7 +897,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Incorrect value and missing argument (ProvidedNonNullArguments)')
      */
-    public function testIncorrectValueAndMissingArgumentProvidedNonNullArguments()
+    public function testIncorrectValueAndMissingArgumentProvidedNonNullArguments() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -913,7 +913,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Null value')
      */
-    public function testNullValue2()
+    public function testNullValue2() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -932,7 +932,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Optional arg, despite required field in type')
      */
-    public function testOptionalArgDespiteRequiredFieldInType()
+    public function testOptionalArgDespiteRequiredFieldInType() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -946,7 +946,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Partial object, only required')
      */
-    public function testPartialObjectOnlyRequired()
+    public function testPartialObjectOnlyRequired() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -960,7 +960,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Partial object, required field can be falsey')
      */
-    public function testPartialObjectRequiredFieldCanBeFalsey()
+    public function testPartialObjectRequiredFieldCanBeFalsey() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -974,7 +974,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Partial object, including required')
      */
-    public function testPartialObjectIncludingRequired()
+    public function testPartialObjectIncludingRequired() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -988,7 +988,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Full object')
      */
-    public function testFullObject()
+    public function testFullObject() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -1008,7 +1008,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Full object with fields in different order')
      */
-    public function testFullObjectWithFieldsInDifferentOrder()
+    public function testFullObjectWithFieldsInDifferentOrder() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -1030,7 +1030,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Partial object, missing required')
      */
-    public function testPartialObjectMissingRequired()
+    public function testPartialObjectMissingRequired() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -1046,7 +1046,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('Partial object, invalid field type')
      */
-    public function testPartialObjectInvalidFieldType()
+    public function testPartialObjectInvalidFieldType() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -1068,7 +1068,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
      * The sorting of equal elements has changed so that the test fails on php < 7
      * @requires PHP 7.0
      */
-    public function testPartialObjectUnknownFieldArg()
+    public function testPartialObjectUnknownFieldArg() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -1095,7 +1095,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('reports original error for custom scalar which throws')
      */
-    public function testReportsOriginalErrorForCustomScalarWhichThrows()
+    public function testReportsOriginalErrorForCustomScalarWhichThrows() : void
     {
         $errors = $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -1120,7 +1120,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('allows custom scalar to accept complex literals')
      */
-    public function testAllowsCustomScalarToAcceptComplexLiterals()
+    public function testAllowsCustomScalarToAcceptComplexLiterals() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -1137,7 +1137,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('with directives of valid types')
      */
-    public function testWithDirectivesOfValidTypes()
+    public function testWithDirectivesOfValidTypes() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         {
@@ -1154,7 +1154,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('with directive with incorrect types')
      */
-    public function testWithDirectiveWithIncorrectTypes()
+    public function testWithDirectiveWithIncorrectTypes() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         {
@@ -1173,7 +1173,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('variables with valid default values')
      */
-    public function testVariablesWithValidDefaultValues()
+    public function testVariablesWithValidDefaultValues() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         query WithDefaultValues(
@@ -1189,7 +1189,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('variables with valid default null values')
      */
-    public function testVariablesWithValidDefaultNullValues()
+    public function testVariablesWithValidDefaultNullValues() : void
     {
         $this->expectPassesRule(new ValuesOfCorrectType, '
         query WithDefaultValues(
@@ -1205,7 +1205,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('variables with invalid default null values')
      */
-    public function testVariablesWithInvalidDefaultNullValues()
+    public function testVariablesWithInvalidDefaultNullValues() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         query WithDefaultValues(
@@ -1225,7 +1225,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('variables with invalid default values')
      */
-    public function testVariablesWithInvalidDefaultValues()
+    public function testVariablesWithInvalidDefaultValues() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         query InvalidDefaultValues(
@@ -1245,7 +1245,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('variables with complex invalid default values')
      */
-    public function testVariablesWithComplexInvalidDefaultValues()
+    public function testVariablesWithComplexInvalidDefaultValues() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         query WithDefaultValues(
@@ -1262,7 +1262,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('complex variables missing required field')
      */
-    public function testComplexVariablesMissingRequiredField()
+    public function testComplexVariablesMissingRequiredField() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         query MissingRequiredField($a: ComplexInput = {intField: 3}) {
@@ -1276,7 +1276,7 @@ class ValuesOfCorrectTypeTest extends ValidatorTestCase
     /**
      * @see it('list variables with invalid item')
      */
-    public function testListVariablesWithInvalidItem()
+    public function testListVariablesWithInvalidItem() : void
     {
         $this->expectFailsRule(new ValuesOfCorrectType, '
         query InvalidItem($a: [String] = ["one", 2]) {
diff --git a/tests/Validator/VariablesAreInputTypesTest.php b/tests/Validator/VariablesAreInputTypesTest.php
index c37a0ee..5031434 100644
--- a/tests/Validator/VariablesAreInputTypesTest.php
+++ b/tests/Validator/VariablesAreInputTypesTest.php
@@ -12,7 +12,7 @@ class VariablesAreInputTypesTest extends ValidatorTestCase
     /**
      * @see it('input types are valid')
      */
-    public function testInputTypesAreValid()
+    public function testInputTypesAreValid() : void
     {
         $this->expectPassesRule(new VariablesAreInputTypes(), '
       query Foo($a: String, $b: [Boolean!]!, $c: ComplexInput) {
@@ -24,7 +24,7 @@ class VariablesAreInputTypesTest extends ValidatorTestCase
     /**
      * @see it('output types are invalid')
      */
-    public function testOutputTypesAreInvalid()
+    public function testOutputTypesAreInvalid() : void
     {
         $this->expectFailsRule(new VariablesAreInputTypes, '
       query Foo($a: Dog, $b: [[CatOrDog!]]!, $c: Pet) {
diff --git a/tests/Validator/VariablesDefaultValueAllowedTest.php b/tests/Validator/VariablesDefaultValueAllowedTest.php
index 0fb543b..468b6a4 100644
--- a/tests/Validator/VariablesDefaultValueAllowedTest.php
+++ b/tests/Validator/VariablesDefaultValueAllowedTest.php
@@ -24,7 +24,7 @@ class VariablesDefaultValueAllowedTest extends ValidatorTestCase
     /**
      * @see it('variables with no default values')
      */
-    public function testVariablesWithNoDefaultValues()
+    public function testVariablesWithNoDefaultValues() : void
     {
         $this->expectPassesRule(new VariablesDefaultValueAllowed(), '
       query NullableValues($a: Int, $b: String, $c: ComplexInput) {
@@ -36,7 +36,7 @@ class VariablesDefaultValueAllowedTest extends ValidatorTestCase
     /**
      * @see it('required variables without default values')
      */
-    public function testRequiredVariablesWithoutDefaultValues()
+    public function testRequiredVariablesWithoutDefaultValues() : void
     {
         $this->expectPassesRule(new VariablesDefaultValueAllowed(), '
       query RequiredValues($a: Int!, $b: String!) {
@@ -48,7 +48,7 @@ class VariablesDefaultValueAllowedTest extends ValidatorTestCase
     /**
      * @see it('variables with valid default values')
      */
-    public function testVariablesWithValidDefaultValues()
+    public function testVariablesWithValidDefaultValues() : void
     {
         $this->expectPassesRule(new VariablesDefaultValueAllowed(), '
       query WithDefaultValues(
@@ -64,7 +64,7 @@ class VariablesDefaultValueAllowedTest extends ValidatorTestCase
     /**
      * @see it('variables with valid default null values')
      */
-    public function testVariablesWithValidDefaultNullValues()
+    public function testVariablesWithValidDefaultNullValues() : void
     {
         $this->expectPassesRule(new VariablesDefaultValueAllowed(), '
       query WithDefaultValues(
@@ -80,7 +80,7 @@ class VariablesDefaultValueAllowedTest extends ValidatorTestCase
     /**
      * @see it('no required variables with default values')
      */
-    public function testNoRequiredVariablesWithDefaultValues()
+    public function testNoRequiredVariablesWithDefaultValues() : void
     {
         $this->expectFailsRule(new VariablesDefaultValueAllowed(), '
       query UnreachableDefaultValues($a: Int! = 3, $b: String! = "default") {
@@ -95,7 +95,7 @@ class VariablesDefaultValueAllowedTest extends ValidatorTestCase
     /**
      * @see it('variables with invalid default null values')
      */
-    public function testNullIntoNullableType()
+    public function testNullIntoNullableType() : void
     {
         $this->expectFailsRule(new VariablesDefaultValueAllowed(), '
       query WithDefaultValues($a: Int! = null, $b: String! = null) {
diff --git a/tests/Validator/VariablesInAllowedPositionTest.php b/tests/Validator/VariablesInAllowedPositionTest.php
index 1defd36..fa8a69a 100644
--- a/tests/Validator/VariablesInAllowedPositionTest.php
+++ b/tests/Validator/VariablesInAllowedPositionTest.php
@@ -12,7 +12,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Boolean => Boolean')
      */
-    public function testBooleanXBoolean()
+    public function testBooleanXBoolean() : void
     {
         // Boolean => Boolean
         $this->expectPassesRule(new VariablesInAllowedPosition(), '
@@ -28,7 +28,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Boolean => Boolean within fragment')
      */
-    public function testBooleanXBooleanWithinFragment()
+    public function testBooleanXBooleanWithinFragment() : void
     {
         // Boolean => Boolean within fragment
         $this->expectPassesRule(new VariablesInAllowedPosition, '
@@ -59,7 +59,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Boolean! => Boolean')
      */
-    public function testBooleanNonNullXBoolean()
+    public function testBooleanNonNullXBoolean() : void
     {
         // Boolean! => Boolean
         $this->expectPassesRule(new VariablesInAllowedPosition, '
@@ -75,7 +75,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Boolean! => Boolean within fragment')
      */
-    public function testBooleanNonNullXBooleanWithinFragment()
+    public function testBooleanNonNullXBooleanWithinFragment() : void
     {
         // Boolean! => Boolean within fragment
         $this->expectPassesRule(new VariablesInAllowedPosition, '
@@ -95,7 +95,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Int => Int! with default')
      */
-    public function testIntXIntNonNullWithDefault()
+    public function testIntXIntNonNullWithDefault() : void
     {
         // Int => Int! with default
         $this->expectPassesRule(new VariablesInAllowedPosition, '
@@ -111,7 +111,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('[String] => [String]')
      */
-    public function testListOfStringXListOfString()
+    public function testListOfStringXListOfString() : void
     {
         $this->expectPassesRule(new VariablesInAllowedPosition, '
       query Query($stringListVar: [String])
@@ -126,7 +126,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('[String!] => [String]')
      */
-    public function testListOfStringNonNullXListOfString()
+    public function testListOfStringNonNullXListOfString() : void
     {
         $this->expectPassesRule(new VariablesInAllowedPosition, '
       query Query($stringListVar: [String!])
@@ -141,7 +141,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('String => [String] in item position')
      */
-    public function testStringXListOfStringInItemPosition()
+    public function testStringXListOfStringInItemPosition() : void
     {
         $this->expectPassesRule(new VariablesInAllowedPosition, '
       query Query($stringVar: String)
@@ -156,7 +156,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('String! => [String] in item position')
      */
-    public function testStringNonNullXListOfStringInItemPosition()
+    public function testStringNonNullXListOfStringInItemPosition() : void
     {
         $this->expectPassesRule(new VariablesInAllowedPosition, '
       query Query($stringVar: String!)
@@ -171,7 +171,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('ComplexInput => ComplexInput')
      */
-    public function testComplexInputXComplexInput()
+    public function testComplexInputXComplexInput() : void
     {
         $this->expectPassesRule(new VariablesInAllowedPosition, '
       query Query($complexVar: ComplexInput)
@@ -186,7 +186,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('ComplexInput => ComplexInput in field position')
      */
-    public function testComplexInputXComplexInputInFieldPosition()
+    public function testComplexInputXComplexInputInFieldPosition() : void
     {
         $this->expectPassesRule(new VariablesInAllowedPosition, '
       query Query($boolVar: Boolean = false)
@@ -201,7 +201,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Boolean! => Boolean! in directive')
      */
-    public function testBooleanNonNullXBooleanNonNullInDirective()
+    public function testBooleanNonNullXBooleanNonNullInDirective() : void
     {
         $this->expectPassesRule(new VariablesInAllowedPosition, '
       query Query($boolVar: Boolean!)
@@ -214,7 +214,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Boolean => Boolean! in directive with default')
      */
-    public function testBooleanXBooleanNonNullInDirectiveWithDefault()
+    public function testBooleanXBooleanNonNullInDirectiveWithDefault() : void
     {
         $this->expectPassesRule(new VariablesInAllowedPosition, '
       query Query($boolVar: Boolean = false)
@@ -227,7 +227,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Int => Int!')
      */
-    public function testIntXIntNonNull()
+    public function testIntXIntNonNull() : void
     {
         $this->expectFailsRule(new VariablesInAllowedPosition, '
       query Query($intArg: Int) {
@@ -246,7 +246,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Int => Int! within fragment')
      */
-    public function testIntXIntNonNullWithinFragment()
+    public function testIntXIntNonNullWithinFragment() : void
     {
         $this->expectFailsRule(new VariablesInAllowedPosition, '
       fragment nonNullIntArgFieldFrag on ComplicatedArgs {
@@ -269,7 +269,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Int => Int! within nested fragment')
      */
-    public function testIntXIntNonNullWithinNestedFragment()
+    public function testIntXIntNonNullWithinNestedFragment() : void
     {
         // Int => Int! within nested fragment
         $this->expectFailsRule(new VariablesInAllowedPosition, '
@@ -298,7 +298,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('String over Boolean')
      */
-    public function testStringOverBoolean()
+    public function testStringOverBoolean() : void
     {
         $this->expectFailsRule(new VariablesInAllowedPosition, '
       query Query($stringVar: String) {
@@ -317,7 +317,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('String => [String]')
      */
-    public function testStringXListOfString()
+    public function testStringXListOfString() : void
     {
         $this->expectFailsRule(new VariablesInAllowedPosition, '
       query Query($stringVar: String) {
@@ -336,7 +336,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('Boolean => Boolean! in directive')
      */
-    public function testBooleanXBooleanNonNullInDirective()
+    public function testBooleanXBooleanNonNullInDirective() : void
     {
         $this->expectFailsRule(new VariablesInAllowedPosition, '
       query Query($boolVar: Boolean) {
@@ -353,7 +353,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('String => Boolean! in directive')
      */
-    public function testStringXBooleanNonNullInDirective()
+    public function testStringXBooleanNonNullInDirective() : void
     {
         // String => Boolean! in directive
         $this->expectFailsRule(new VariablesInAllowedPosition, '
@@ -371,7 +371,7 @@ class VariablesInAllowedPositionTest extends ValidatorTestCase
     /**
      * @see it('[String] => [String!]')
      */
-    public function testStringArrayXStringNonNullArray()
+    public function testStringArrayXStringNonNullArray() : void
     {
         $this->expectFailsRule(
             new VariablesInAllowedPosition,