Enabled subscriptions in executor

src/Executor/Executor.php

@@ -196,9 +196,18 @@ class Executor
                     );
                 }
                 return $mutationType;
+            case 'subscription':
+                $subscriptionType = $schema->getSubscriptionType();
+                if (!$subscriptionType) {
+                    throw new Error(
+                        'Schema is not configured for subscriptions',
+                        [ $operation ]
+                    );
+                }
+                return $subscriptionType;
             default:
                 throw new Error(
-                    'Can only execute queries and mutations',
+                    'Can only execute queries, mutations and subscriptions',
                     [$operation]
                 );
         }

tests/Type/EnumTypeTest.php

@@ -218,10 +218,8 @@ class EnumTypeTest extends \PHPUnit_Framework_TestCase
      */
     public function testAcceptsEnumLiteralsAsInputArgumentsToSubscriptions()
     {
-        $this->markTestIncomplete('Enable when subscription support is implemented');
-
         $this->assertEquals(
-            ['data' => ['subscribeToEnum' => 'GREEN'], 'errors' => [[]]],
+            ['data' => ['subscribeToEnum' => 'GREEN']],
             GraphQL::execute(
                 $this->schema,
                 'subscription x($color: Color!) { subscribeToEnum(color: $color) }',