diff --git a/src/Type/Definition/CustomScalarType.php b/src/Type/Definition/CustomScalarType.php
new file mode 100644
index 0000000..0893c27
--- /dev/null
+++ b/src/Type/Definition/CustomScalarType.php
@@ -0,0 +1,30 @@
+<?php
+namespace GraphQL\Type\Definition;
+
+
+class CustomScalarType extends ScalarType
+{
+    private $config;
+
+    function __construct(array $config)
+    {
+        $this->name = $config['name'];
+        $this->config = $config;
+        parent::__construct();
+    }
+
+    public function serialize($value)
+    {
+        return call_user_func($this->config['serialize'], $value);
+    }
+
+    public function parseValue($value)
+    {
+        return call_user_func($this->config['parseValue'], $value);
+    }
+
+    public function parseLiteral(/* GraphQL\Language\AST\Value */ $valueAST)
+    {
+        return call_user_func($this->config['parseLiteral'], $valueAST);
+    }
+}
diff --git a/tests/Type/DefinitionTest.php b/tests/Type/DefinitionTest.php
index ef0de37..767535d 100644
--- a/tests/Type/DefinitionTest.php
+++ b/tests/Type/DefinitionTest.php
@@ -39,6 +39,11 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
      */
     public $blogQuery;
 
+    /**
+     * @var ObjectType
+     */
+    public $blogSubscription;
+
     /**
      * @var ObjectType
      */
@@ -124,11 +129,28 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
                 'writeArticle' => ['type' => $this->blogArticle]
             ]
         ]);
+
+        $this->blogSubscription = new ObjectType([
+            'name' => 'Subscription',
+            'fields' => [
+                'articleSubscribe' => [
+                    'args' => [ 'id' => [ 'type' => Type::string() ]],
+                    'type' => $this->blogArticle
+                ]
+            ]
+        ]);
     }
 
+    // Type System: Example
+
+    /**
+     * @it defines a query only schema
+     */
     public function testDefinesAQueryOnlySchema()
     {
-        $blogSchema = new Schema($this->blogQuery);
+        $blogSchema = new Schema([
+            'query' => $this->blogQuery
+        ]);
 
         $this->assertSame($blogSchema->getQueryType(), $this->blogQuery);
 
@@ -165,9 +187,15 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
         $this->assertSame($this->blogArticle, $feedFieldType->getWrappedType());
     }
 
+    /**
+     * @it defines a mutation schema
+     */
     public function testDefinesAMutationSchema()
     {
-        $schema = new Schema($this->blogQuery, $this->blogMutation);
+        $schema = new Schema([
+            'query' => $this->blogQuery,
+            'mutation' => $this->blogMutation
+        ]);
 
         $this->assertSame($this->blogMutation, $schema->getMutationType());
         $writeMutation = $this->blogMutation->getField('writeArticle');
@@ -178,6 +206,27 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
         $this->assertSame('writeArticle', $writeMutation->name);
     }
 
+    /**
+     * @it defines a subscription schema
+     */
+    public function testDefinesSubscriptionSchema()
+    {
+        $schema = new Schema([
+            'query' => $this->blogQuery,
+            'subscription' => $this->blogSubscription
+        ]);
+
+        $this->assertEquals($this->blogSubscription, $schema->getSubscriptionType());
+
+        $sub = $this->blogSubscription->getField('articleSubscribe');
+        $this->assertEquals($sub->getType(), $this->blogArticle);
+        $this->assertEquals($sub->getType()->name, 'Article');
+        $this->assertEquals($sub->name, 'articleSubscribe');
+    }
+
+    /**
+     * @it includes nested input objects in the map
+     */
     public function testIncludesNestedInputObjectInTheMap()
     {
         $nestedInputObject = new InputObjectType([
@@ -198,10 +247,16 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
             ]
         ]);
 
-        $schema = new Schema($this->blogQuery, $someMutation);
+        $schema = new Schema([
+            'query' => $this->blogQuery,
+            'mutation' => $someMutation
+        ]);
         $this->assertSame($nestedInputObject, $schema->getType('NestedInputObject'));
     }
 
+    /**
+     * @it includes interfaces\' subtypes in the type map
+     */
     public function testIncludesInterfaceSubtypesInTheTypeMap()
     {
         $someInterface = new InterfaceType([
@@ -220,18 +275,23 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
             'isTypeOf' => function() {return true;}
         ]);
 
-        $schema = new Schema(new ObjectType([
-            'name' => 'Query',
-            'fields' => [
-                'iface' => ['type' => $someInterface]
-            ]
-        ]));
+        $schema = new Schema([
+            'query' => new ObjectType([
+                'name' => 'Query',
+                'fields' => [
+                    'iface' => ['type' => $someInterface]
+                ]
+            ]),
+            'types' => [$someSubtype]
+        ]);
         $this->assertSame($someSubtype, $schema->getType('SomeSubtype'));
     }
 
+    /**
+     * @it includes interfaces\' thunk subtypes in the type map
+     */
     public function testIncludesInterfacesThunkSubtypesInTheTypeMap()
     {
-        // includes interfaces' thunk subtypes in the type map
         $someInterface = null;
 
         $someSubtype = new ObjectType([
@@ -250,16 +310,22 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
             ]
         ]);
 
-        $schema = new Schema(new ObjectType([
-            'name' => 'Query',
-            'fields' => [
-                'iface' => ['type' => $someInterface]
-            ]
-        ]));
+        $schema = new Schema([
+            'query' => new ObjectType([
+                'name' => 'Query',
+                'fields' => [
+                    'iface' => ['type' => $someInterface]
+                ]
+            ]),
+            'types' => [$someSubtype]
+        ]);
 
         $this->assertSame($someSubtype, $schema->getType('SomeSubtype'));
     }
 
+    /**
+     * @it stringifies simple types
+     */
     public function testStringifiesSimpleTypes()
     {
         $this->assertSame('Int', (string) Type::int());
@@ -278,6 +344,9 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
         $this->assertSame('[[Int]]', (string) new ListOfType(new ListOfType(Type::int())));
     }
 
+    /**
+     * @it identifies input types
+     */
     public function testIdentifiesInputTypes()
     {
         $expected = [
@@ -294,6 +363,9 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
         }
     }
 
+    /**
+     * @it identifies output types
+     */
     public function testIdentifiesOutputTypes()
     {
         $expected = [
@@ -310,12 +382,18 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
         }
     }
 
+    /**
+     * @it prohibits nesting NonNull inside NonNull
+     */
     public function testProhibitsNonNullNesting()
     {
         $this->setExpectedException('\Exception');
         new NonNull(new NonNull(Type::int()));
     }
 
+    /**
+     * @it prohibits putting non-Object types in unions
+     */
     public function testProhibitsPuttingNonObjectTypesInUnions()
     {
         $int = Type::int();
@@ -387,12 +465,15 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
             }
         ]);
 
-        $schema = new Schema(new ObjectType([
-            'name' => 'Query',
-            'fields' => [
-                'node' => ['type' => $node]
-            ]
-        ]));
+        $schema = new Schema([
+            'query' => new ObjectType([
+                'name' => 'Query',
+                'fields' => [
+                    'node' => ['type' => $node]
+                ]
+            ]),
+            'types' => [$user, $blog]
+        ]);
 
         $this->assertTrue($called);
 
@@ -429,7 +510,10 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
             ]
         ]);
 
-        $schema = new Schema($this->blogQuery, $someMutation);
+        $schema = new Schema([
+            'query' => $this->blogQuery,
+            'mutation' => $someMutation
+        ]);
 
         $this->assertTrue($called);
         $this->assertSame($inputObject, $schema->getType('InputObject'));
@@ -459,7 +543,9 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
             ]
         ]);
 
-        $schema = new Schema($query);
+        $schema = new Schema([
+            'query' => $query
+        ]);
 
         $this->assertTrue($called);
         $this->assertSame($interface, $schema->getType('SomeInterface'));
diff --git a/tests/Type/EnumTypeTest.php b/tests/Type/EnumTypeTest.php
new file mode 100644
index 0000000..a7f2be2
--- /dev/null
+++ b/tests/Type/EnumTypeTest.php
@@ -0,0 +1,306 @@
+<?php
+namespace GraphQL\Tests\Type;
+
+use GraphQL\Error;
+use GraphQL\GraphQL;
+use GraphQL\Schema;
+use GraphQL\Type\Definition\EnumType;
+use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Type\Definition\Type;
+
+class EnumTypeTest extends \PHPUnit_Framework_TestCase
+{
+    private $schema;
+
+    public function setUp()
+    {
+        $ColorType = new EnumType([
+            'name' => 'Color',
+            'values' => [
+                'RED' => ['value' => 0],
+                'GREEN' => ['value' => 1],
+                'BLUE' => ['value' => 2],
+            ]
+        ]);
+
+        $QueryType = new ObjectType([
+            'name' => 'Query',
+            'fields' => [
+                'colorEnum' => [
+                    'type' => $ColorType,
+                    'args' => [
+                        'fromEnum' => ['type' => $ColorType],
+                        'fromInt' => ['type' => Type::int()],
+                        'fromString' => ['type' => Type::string()],
+                    ],
+                    'resolve' => function ($value, $args) {
+                        if (isset($args['fromInt'])) {
+                            return $args['fromInt'];
+                        }
+                        if (isset($args['fromString'])) {
+                            return $args['fromString'];
+                        }
+                        if (isset($args['fromEnum'])) {
+                            return $args['fromEnum'];
+                        }
+                    }
+                ],
+                'colorInt' => [
+                    'type' => Type::int(),
+                    'args' => [
+                        'fromEnum' => ['type' => $ColorType],
+                        'fromInt' => ['type' => Type::int()],
+                    ],
+                    'resolve' => function ($value, $args) {
+                        if (isset($args['fromInt'])) {
+                            return $args['fromInt'];
+                        }
+                        if (isset($args['fromEnum'])) {
+                            return $args['fromEnum'];
+                        }
+                    }
+                ]
+            ]
+        ]);
+
+        $MutationType = new ObjectType([
+            'name' => 'Mutation',
+            'fields' => [
+                'favoriteEnum' => [
+                    'type' => $ColorType,
+                    'args' => ['color' => ['type' => $ColorType]],
+                    'resolve' => function ($value, $args) {
+                        return isset($args['color']) ? $args['color'] : null;
+                    }
+                ]
+            ]
+        ]);
+
+        $SubscriptionType = new ObjectType([
+            'name' => 'Subscription',
+            'fields' => [
+                'subscribeToEnum' => [
+                    'type' => $ColorType,
+                    'args' => ['color' => ['type' => $ColorType]],
+                    'resolve' => function ($value, $args) {
+                        return isset($args['color']) ? $args['color'] : null;
+                    }
+                ]
+            ]
+        ]);
+
+        $this->schema = new Schema([
+            'query' => $QueryType,
+            'mutation' => $MutationType,
+            'subscription' => $SubscriptionType
+        ]);
+    }
+
+    // Describe: Type System: Enum Values
+
+    /**
+     * @it accepts enum literals as input
+     */
+    public function testAcceptsEnumLiteralsAsInput()
+    {
+        $this->assertEquals(
+            ['data' => ['colorInt' => 1]],
+            GraphQL::execute($this->schema, '{ colorInt(fromEnum: GREEN) }')
+        );
+    }
+
+    /**
+     * @it enum may be output type
+     */
+    public function testEnumMayBeOutputType()
+    {
+        $this->assertEquals(
+            ['data' => ['colorEnum' => 'GREEN']],
+            GraphQL::execute($this->schema, '{ colorEnum(fromInt: 1) }')
+        );
+    }
+
+    /**
+     * @it enum may be both input and output type
+     */
+    public function testEnumMayBeBothInputAndOutputType()
+    {
+        $this->assertEquals(
+            ['data' => ['colorEnum' => 'GREEN']],
+            GraphQL::execute($this->schema, '{ colorEnum(fromEnum: GREEN) }')
+        );
+    }
+
+    /**
+     * @it does not accept string literals
+     */
+    public function testDoesNotAcceptStringLiterals()
+    {
+        $this->expectFailure(
+            '{ colorEnum(fromEnum: "GREEN") }',
+            null,
+            "Argument \"fromEnum\" has invalid value \"GREEN\".\nExpected type \"Color\", found \"GREEN\"."
+        );
+    }
+
+    /**
+     * @it does not accept incorrect internal value
+     */
+    public function testDoesNotAcceptIncorrectInternalValue()
+    {
+        $this->assertEquals(
+            ['data' => ['colorEnum' => null]],
+            GraphQL::execute($this->schema, '{ colorEnum(fromString: "GREEN") }')
+        );
+    }
+
+    /**
+     * @it does not accept internal value in place of enum literal
+     */
+    public function testDoesNotAcceptInternalValueInPlaceOfEnumLiteral()
+    {
+        $this->expectFailure(
+            '{ colorEnum(fromEnum: 1) }',
+            null,
+            "Argument \"fromEnum\" has invalid value 1.\nExpected type \"Color\", found 1."
+        );
+    }
+
+    /**
+     * @it does not accept enum literal in place of int
+     */
+    public function testDoesNotAcceptEnumLiteralInPlaceOfInt()
+    {
+        $this->expectFailure(
+            '{ colorEnum(fromInt: GREEN) }',
+            null,
+            "Argument \"fromInt\" has invalid value GREEN.\nExpected type \"Int\", found GREEN."
+        );
+    }
+
+    /**
+     * @it accepts JSON string as enum variable
+     */
+    public function testAcceptsJSONStringAsEnumVariable()
+    {
+        $this->assertEquals(
+            ['data' => ['colorEnum' => 'BLUE']],
+            GraphQL::execute(
+                $this->schema,
+                'query test($color: Color!) { colorEnum(fromEnum: $color) }',
+                null,
+                ['color' => 'BLUE']
+            )
+        );
+    }
+
+    /**
+     * @it accepts enum literals as input arguments to mutations
+     */
+    public function testAcceptsEnumLiteralsAsInputArgumentsToMutations()
+    {
+        $this->assertEquals(
+            ['data' => ['favoriteEnum' => 'GREEN']],
+            GraphQL::execute(
+                $this->schema,
+                'mutation x($color: Color!) { favoriteEnum(color: $color) }',
+                null,
+                ['color' => 'GREEN']
+            )
+        );
+    }
+
+    /**
+     * @it accepts enum literals as input arguments to subscriptions
+     * @todo
+     */
+    public function testAcceptsEnumLiteralsAsInputArgumentsToSubscriptions()
+    {
+        $this->markTestIncomplete('Enable when subscription support is implemented');
+
+        $this->assertEquals(
+            ['data' => ['subscribeToEnum' => 'GREEN'], 'errors' => [[]]],
+            GraphQL::execute(
+                $this->schema,
+                'subscription x($color: Color!) { subscribeToEnum(color: $color) }',
+                null,
+                ['color' => 'GREEN']
+            )
+        );
+    }
+
+    /**
+     * @it does not accept internal value as enum variable
+     */
+    public function testDoesNotAcceptInternalValueAsEnumVariable()
+    {
+        $this->expectFailure(
+            'query test($color: Color!) { colorEnum(fromEnum: $color) }',
+            ['color' => 2],
+            "Variable \"\$color\" got invalid value 2.\nExpected type \"Color\", found 2."
+        );
+    }
+
+    /**
+     * @it does not accept string variables as enum input
+     */
+    public function testDoesNotAcceptStringVariablesAsEnumInput()
+    {
+        $this->expectFailure(
+            'query test($color: String!) { colorEnum(fromEnum: $color) }',
+            ['color' => 'BLUE'],
+            'Variable "$color" of type "String!" used in position expecting type "Color".'
+        );
+    }
+
+    /**
+     * @it does not accept internal value variable as enum input
+     */
+    public function testDoesNotAcceptInternalValueVariableSsEnumInput()
+    {
+        $this->expectFailure(
+            'query test($color: Int!) { colorEnum(fromEnum: $color) }',
+            ['color' => 2],
+            'Variable "$color" of type "Int!" used in position ' . 'expecting type "Color".'
+        );
+    }
+
+    /**
+     * @it enum value may have an internal value of 0
+     */
+    public function testEnumValueMayHaveAnInternalValueOf0()
+    {
+        $this->assertEquals(
+            ['data' => ['colorEnum' => 'RED', 'colorInt' => 0]],
+            GraphQL::execute($this->schema, "{
+                colorEnum(fromEnum: RED)
+                colorInt(fromEnum: RED)
+            }")
+        );
+    }
+
+    /**
+     * @it enum inputs may be nullable
+     */
+    public function testEnumInputsMayBeNullable()
+    {
+        $this->assertEquals(
+            ['data' => ['colorEnum' => null, 'colorInt' => null]],
+            GraphQL::execute($this->schema, "{
+                colorEnum
+                colorInt
+            }")
+        );
+    }
+
+    private function expectFailure($query, $vars, $err)
+    {
+        $result = GraphQL::executeAndReturnResult($this->schema, $query, null, $vars);
+        $this->assertEquals(1, count($result->errors));
+
+        $this->assertEquals(
+            $err,
+            $result->errors[0]->getMessage()
+        );
+    }
+}
diff --git a/tests/Type/ScalarSerializationTest.php b/tests/Type/ScalarSerializationTest.php
index 83af55d..21f0864 100644
--- a/tests/Type/ScalarSerializationTest.php
+++ b/tests/Type/ScalarSerializationTest.php
@@ -5,38 +5,57 @@ use GraphQL\Type\Definition\Type;
 
 class ScalarSerializationTest extends \PHPUnit_Framework_TestCase
 {
-    public function testCoercesOutputInt()
+    // Type System: Scalar coercion
+
+    /**
+     * @it serializes output int
+     */
+    public function testSerializesOutputInt()
     {
         $intType = Type::int();
 
         $this->assertSame(1, $intType->serialize(1));
         $this->assertSame(0, $intType->serialize(0));
+        $this->assertSame(-1, $intType->serialize(-1));
         $this->assertSame(0, $intType->serialize(0.1));
         $this->assertSame(1, $intType->serialize(1.1));
         $this->assertSame(-1, $intType->serialize(-1.1));
         $this->assertSame(100000, $intType->serialize(1e5));
+        // Maybe a safe PHP int, but bigger than 2^32, so not
+        // representable as a GraphQL Int
+        $this->assertSame(null, $intType->serialize(9876504321));
+        $this->assertSame(null, $intType->serialize(-9876504321));
         $this->assertSame(null, $intType->serialize(1e100));
         $this->assertSame(null, $intType->serialize(-1e100));
         $this->assertSame(-1, $intType->serialize('-1.1'));
         $this->assertSame(null, $intType->serialize('one'));
         $this->assertSame(0, $intType->serialize(false));
+        $this->assertSame(1, $intType->serialize(true));
     }
 
-    public function testCoercesOutputFloat()
+    /**
+     * @it serializes output float
+     */
+    public function testSerializesOutputFloat()
     {
         $floatType = Type::float();
 
         $this->assertSame(1.0, $floatType->serialize(1));
+        $this->assertSame(0.0, $floatType->serialize(0));
         $this->assertSame(-1.0, $floatType->serialize(-1));
         $this->assertSame(0.1, $floatType->serialize(0.1));
         $this->assertSame(1.1, $floatType->serialize(1.1));
         $this->assertSame(-1.1, $floatType->serialize(-1.1));
+        $this->assertSame(-1.1, $floatType->serialize('-1.1'));
         $this->assertSame(null, $floatType->serialize('one'));
         $this->assertSame(0.0, $floatType->serialize(false));
         $this->assertSame(1.0, $floatType->serialize(true));
     }
 
-    public function testCoercesOutputStrings()
+    /**
+     * @it serializes output strings
+     */
+    public function testSerializesOutputStrings()
     {
         $stringType = Type::string();
 
@@ -47,12 +66,16 @@ class ScalarSerializationTest extends \PHPUnit_Framework_TestCase
         $this->assertSame('false', $stringType->serialize(false));
     }
 
-    public function testCoercesOutputBoolean()
+    /**
+     * @it serializes output boolean
+     */
+    public function testSerializesOutputBoolean()
     {
         $boolType = Type::boolean();
 
         $this->assertSame(true, $boolType->serialize('string'));
         $this->assertSame(false, $boolType->serialize(''));
+        $this->assertSame(true, $boolType->serialize('1'));
         $this->assertSame(true, $boolType->serialize(1));
         $this->assertSame(false, $boolType->serialize(0));
         $this->assertSame(true, $boolType->serialize(true));