无法读取 Angular 测试模拟的属性“订阅”

Question

我正在尝试对具有注入服务的 Angular 组件进行单元测试。在组件的构造函数中，调用注入服务的一个方法，该方法返回一个 Observable。我试图在组件的单​​元测试中模拟该服务，但我一直遇到此错误：TypeError: Cannot read property 'subscribe' of undefined。

我尝试通过以下方式模拟服务：

const serviceStub = {
  getObservable: () => { return {subscribe: () => {}}; },
};

beforeEach(async(() => {
  TestBed.configureTestingModule({
    providers: [
      {provide: MyService, useValue: serviceStub}
    ]
})


it('should create', () => {
  spyOn(serviceStub, 'getObservable').and.returnValue({subscribe: () => {}});
  expect(component).toBeTruthy();
});

感觉好像我错过了一些明显的东西。有人能指出来吗？

更新

即使我在我的测试平台提供程序中注入实际服务，我也会收到此错误。

组件的构造函数如下所示：

private _subscription: Subscription;

constructor(private _service: MyService) {
  this._subscription = _service.getObservable().subscribe(console.log);
}

Answer 1

使用inject 注入服务并模拟它而不是存根

it('should create', inject([MyService], (myService: MyService) => {
  spyOn(myService, 'getObservable').and.returnValue({subscribe: () => {}});
  expect(component).toBeTruthy();
}));

这里是完整版：

组件：

@Component({
  selector: 'my-cmp',
  template: 'my cmp {{x}}'
})
export class MyComponent {
  x;

  constructor(private myService: MyService) {
    this.myService.getObservable()
      .subscribe(x => {
        console.log(x);
        this.x = x;
      });
  }
}

测试：

   describe('my component test', () => {
    let fixture: ComponentFixture<MyComponent>, comp: MyComponent, debugElement: DebugElement, element: HTMLElement;

    beforeEach(async(() => {
      TestBed.configureTestingModule({
        declarations: [MyComponent],
        providers: [MyService]
      });
    }));

    beforeEach(() => {
      fixture = TestBed.createComponent(MyComponent);
      comp = fixture.componentInstance;
      debugElement = fixture.debugElement;
      element = debugElement.nativeElement;
    });

    it('should create', inject([MyService], (myService: MyService) => {
      expect(comp).toBeTruthy();
    }));

    it('should set value', async(inject([MyService], (myService: MyService) => {
      spyOn(myService, 'getObservable').and.returnValue(Observable.of(1));

      fixture.detectChanges();

      fixture.whenStable().then(() => {
        expect(comp.x).toEqual(1);
      });
    })));
  });