Add extensions to typescript integration test

Author: benjie

integrationTests/ts/index.ts

@@ -2,17 +2,58 @@ import { GraphQLString, GraphQLSchema, GraphQLObjectType } from 'graphql/type';
 import { ExecutionResult } from 'graphql/execution';
 import { graphqlSync } from 'graphql';
 
+interface SomeExtension {
+  number: number;
+  string: string;
+}
+
+const example: SomeExtension = {
+  number: 42,
+  string: 'Meaning of life',
+};
+
+// The following code block requires a newer version of TypeScript
+/*! >=3.2
+
+declare module 'graphql' {
+  interface GraphQLObjectTypeExtensions<TSource = any, TContext = any> {
+    someObjectExtension?: SomeExtension;
+  }
+  interface GraphQLFieldExtensions<
+    TSource,
+    TContext,
+    TArgs = { [argName: string]: any }
+  > {
+    someFieldExtension?: SomeExtension;
+  }
+  interface GraphQLArgumentExtensions {
+    someArgumentExtension?: SomeExtension;
+  }
+}
+*/
+
 const queryType: GraphQLObjectType = new GraphQLObjectType({
   name: 'Query',
   fields: {
     sayHi: {
       type: GraphQLString,
       args: {
-        who: { type: GraphQLString },
+        who: {
+          type: GraphQLString,
+          extensions: {
+            someArgumentExtension: example,
+          },
+        },
       },
       resolve: (_root, args) => 'Hello ' + (args.who || 'World'),
+      extensions: {
+        someFieldExtension: example,
+      },
     },
   },
+  extensions: {
+    someObjectExtension: example,
+  },
 });
 
 const schema: GraphQLSchema = new GraphQLSchema({