Update printSchema for recent SDL change to implements.

Added test to prevent future regressions. Updated existing also.

Author: mohawk2

src/utilities/__tests__/extendSchema-test.js

@@ -697,7 +697,7 @@ describe('extendSchema', () => {
         fizz: String
       }
 
-      type Foo implements SomeInterface, NewInterface {
+      type Foo implements SomeInterface & NewInterface {
         name: String
         some: SomeInterface
         tree: [Foo]!
@@ -761,7 +761,7 @@ describe('extendSchema', () => {
         foo: Foo
       }
 
-      type Biz implements NewInterface, SomeInterface {
+      type Biz implements NewInterface & SomeInterface {
         fizz: String
         buzz: String
         name: String

src/utilities/__tests__/schemaPrinter-test.js

@@ -9,6 +9,7 @@ import { describe, it } from 'mocha';
 import { expect } from 'chai';
 import dedent from '../../jsutils/dedent';
 import { printSchema, printIntrospectionSchema } from '../schemaPrinter';
+import { buildSchema } from '../buildASTSchema';
 import {
   GraphQLSchema,
   GraphQLInputObjectType,
@@ -27,7 +28,10 @@ import { GraphQLDirective } from '../../type/directives';
 import { DirectiveLocation } from '../../language/directiveLocation';
 
 function printForTest(schema) {
-  return printSchema(schema);
+  const schemaText = printSchema(schema);
+  // keep printSchema and buildSchema in sync
+  expect(printSchema(buildSchema(schemaText))).to.equal(schemaText);
+  return schemaText;
 }
 
 function printSingleFieldSchema(fieldConfig) {
@@ -388,7 +392,7 @@ describe('Type System Printer', () => {
         int: Int
       }
 
-      type Bar implements Foo, Baaz {
+      type Bar implements Foo & Baaz {
         str: String
         int: Int
       }

src/utilities/schemaPrinter.js

@@ -176,7 +176,7 @@ function printScalar(type: GraphQLScalarType, options): string {
 function printObject(type: GraphQLObjectType, options): string {
   const interfaces = type.getInterfaces();
   const implementedInterfaces = interfaces.length
-    ? ' implements ' + interfaces.map(i => i.name).join(', ')
+    ? ' implements ' + interfaces.map(i => i.name).join(' & ')
     : '';
   return (
     printDescription(options, type) +