Angular 2 RC6测试：TypeError：无法读取null的属性'injector'

Question

在搜索解决方案几个小时后，我在测试angular2应用程序时仍然遇到以下错误：

TypeError: Cannot read property 'injector' of null
        at TestBed._createCompilerAndModule (webpack:///~/@angular/core/testing/test_bed.js:247:0 <- config/spec-bundle.js:66075:44)
        at TestBed._initIfNeeded (webpack:///~/@angular/core/testing/test_bed.js:213:0 <- config/spec-bundle.js:66041:39)
        at TestBed.execute (webpack:///~/@angular/core/testing/test_bed.js:275:0 <- config/spec-bundle.js:66103:14)
        at Object.<anonymous> (webpack:///~/@angular/core/testing/test_bed.js:367:28 <- config/spec-bundle.js:66195:45)
        at ZoneDelegate.invoke (webpack:///~/zone.js/dist/zone.js:332:0 <- config/spec-bundle.js:55179:29)
        at ProxyZoneSpec.onInvoke (webpack:///~/zone.js/dist/proxy.js:106:0 <- config/spec-bundle.js:54712:44)
        at ZoneDelegate.invoke (webpack:///~/zone.js/dist/zone.js:331:0 <- config/spec-bundle.js:55178:35)
        at Zone.run (webpack:///~/zone.js/dist/zone.js:225:0 <- config/spec-bundle.js:55072:44)
        at Object.<anonymous> (webpack:///~/zone.js/dist/jasmine-patch.js:123:28 <- config/spec-bundle.js:54391:51)
        at ZoneQueueRunner.jasmine.QueueRunner.ZoneQueueRunner.execute (webpack:///~/zone.js/dist/jasmine-patch.js:151:0 <- config/spec-bundle.js:54419:43)
        at ZoneQueueRunner.jasmine.QueueRunner.ZoneQueueRunner.execute (webpack:///~/zone.js/dist/jasmine-patch.js:151:0 <- config/spec-bundle.js:54419:43)
        at ZoneDelegate.invokeTask (webpack:///~/zone.js/dist/zone.js:365:0 <- config/spec-bundle.js:55212:38)
        at Zone.runTask (webpack:///~/zone.js/dist/zone.js:265:0 <- config/spec-bundle.js:55112:48)
        at drainMicroTaskQueue (webpack:///~/zone.js/dist/zone.js:497:0 <- config/spec-bundle.js:55344:36)
        at ZoneTask.invoke (webpack:///~/zone.js/dist/zone.js:437:0 <- config/spec-bundle.js:55284:26)

这是我的测试文件：

describe('Widget service', () => {
  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [
        BaseRequestOptions,
        MockBackend,
        {
          provide: Http, useFactory: (backend: ConnectionBackend, defaultOptions: BaseRequestOptions) => {
          return new Http(backend, defaultOptions);
        }, deps: [MockBackend, BaseRequestOptions]
        },
        {provide: WidgetService, useClass: WidgetService}
      ]
    });
  });

  it('should retrieve widgets by id',
    inject([WidgetService, MockBackend], fakeAsync((widgetService: WidgetService, mockBackend: MockBackend) => {
      let res: Response;
      mockBackend.connections.subscribe(c => {
        expect(c.request.url).toBe('src/app/assets/widget_00000011.json');
        let response = new ResponseOptions({body: '[{"id": "00000011", "displayName":"My NevisReports Server"}]'});
        c.mockRespond(new Response(response));
      });
      widgetService.getWidgetById('00000011').subscribe((response) => {
        res = response;
      });
      expect(res[0].id).toBe('00000011');
    }))
  );

});

我的服务如下：

@Injectable()
export class WidgetService {

  widgets: any[];
  baseURL: string = 'http://localhost:8080/patterns/';
  constructor(private http: Http) {}

  getWidgetById(id: string) {
    return this.http.get(`/app/assets/widget_${id}.json`)
      .map(
        (res:Response) =>
          res.json()
      );
  }

  private handleError(error: any) {
    console.error('An error occurred', error);
    return Promise.reject(error.message || error);
  }
}

我也在使用webpack，我称之为initTestEnvironment。