如何在angular onInit方法中測試subscribe函數？

Question

我有以下要測試的組件：

零件：

 constructor(
    private countrystore: Store<CountryAppState>,
    private docstore: Store<DocumentAppState>,
    private formBuilder: FormBuilder,
  ) {}

  ngOnInit() {
    this.getCountryState = this.countrystore.select('selecttimaticCountryState');

    this.getCountryState.subscribe((state) => {
      this.countries = state.response;
    });

規格文件：

describe('TravellerInfoComponent', () => {
  let component: TravellerInfoComponent;
  let fixture: ComponentFixture<TravellerInfoComponent>;

  Object.defineProperty(window, "matchMedia", {
    value: jest.fn(() => { return { matches: true } })
  });

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [
        StoreModule.forRoot({}),
        EffectsModule.forRoot([]),
        BrowserAnimationsModule,
        HttpClientModule
      ],
      providers: [
        FormsModule
      ]
    })
    .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(TravellerInfoComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });

在我甚至可以編寫測試之前，我收到以下錯誤：

我看過類似的答案，建議使用'of'rxjs運算符來模擬一個observable，其他建議使用spyOn技術。 但是我不太明白應該在哪里插入。 對測試菜鳥的任何幫助都會很棒。

Answer 1

const countrystore = TestBed.get(Store<CountryAppState>);
spyOn(countrystore, 'select').and.callFake(() => {
  return of(someTestDataYouCreate);
});