fix(amplify-appsync-simulator): string functions not called on items … (

aws-amplify#7636)

* fix(amplify-appsync-simulator): string functions not called on items of JavaArray<string> in the resolvers

* feat(amplify-appsync-simulator): added toJavaString that accepts a string and returns a JavaString

* feat(amplify-appsync-simulator): map.keySet returns an a JavaArray with elements of type JavaString

* feat(amplify-appsync-simulator): using this.mapper in map.keySet

packages/amplify-appsync-simulator/src/__tests__/velocity/value-mapper/map.test.ts

@@ -1,4 +1,7 @@
+import { JavaArray } from './../../../velocity/value-mapper/array';
 import { JavaMap } from '../../../velocity/value-mapper/map';
+import { JavaString } from '../../../velocity/value-mapper/string';
+import { map as mapper } from '../../../velocity/value-mapper/mapper';
 
 describe('JavaMap', () => {
   let identityMapper = jest.fn().mockImplementation(val => val);
@@ -66,6 +69,12 @@ describe('JavaMap', () => {
     expect(map.keySet().toJSON()).toEqual(['foo', 'bar']);
   });
 
+  it('keySet returns a JavaArray with each element of type JavaString', () => {
+    const obj = { foo: 'Foo Value', bar: 'Bar Value' };
+    const map = new JavaMap(obj, mapper);
+    expect(map.keySet()).toEqual(new JavaArray([new JavaString('foo'), new JavaString('bar')], mapper));
+  });
+
   it('put', () => {
     const map = new JavaMap({}, identityMapper);
     map.put('foo', 'Foo Value');

packages/amplify-appsync-simulator/src/velocity/value-mapper/map.ts

@@ -56,7 +56,7 @@ export class JavaMap {
   }
 
   keySet() {
-    return new JavaArray(Array.from(this.map.keys()), this.mapper);
+    return new JavaArray(Array.from(this.map.keys()).map(this.mapper as any), this.mapper);
   }
 
   put(key, value) {