无法通过单元测试读取ngOnInit内部subscribe的未定义属性(读取'subscribe')

当前面临单元测试错误:

AppComponent > should call app
TypeError: Cannot read properties of undefined (reading 'subscribe')

在我的ngOnInit中,我有:

this.eventsService.currentEvents.subscribe(events => {
  this.events = events;
  return this.processEvents(this.events);
});

失败的测试就在这里(这里称为ngOnInit):

  it(`should call app`, () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.debugElement.componentInstance;
    app.ngOnInit();
  });

我的活动服务是:

export class EventsService {
  constructor(private http: HttpClient, private store: Store<AppState>) {}
  
  private eventsSource = new BehaviorSubject<any>([]);
  currentEvents: Observable<any> = this.eventsSource .asObservable();
  
  getEvents(events: []) {
   this.eventsSource.next(events);
  }
}

应用程序。组成部分spec也有这样的设置:

  beforeEach(waitForAsync(() => {
    TestBed.configureTestingModule({
      imports: [RouterTestingModule, HttpClientModule],
      declarations: [AppComponent],
      providers: [
        { provide: EventsService , useValue: {
          getEvents: () => of([]),
          processEvents: () => of([])
        }},
        provideMockStore({}),
        { provide: Angulartics2, useValue: {} },
        { provide: Angulartics2GoogleAnalytics, useValue: { startTracking: () => {}} },
        { provide: WindowRef }
      ],
      schemas: [CUSTOM_ELEMENTS_SCHEMA]
    }).compileComponents();
  }));

  beforeEach(() => {
    eventService = TestBed.inject(EventsService);
    (<any>window).ga = jasmine.createSpy('ga');
  });