如何在 Jasmine/Angular 中模拟服务的事件发射器

Question

我正在尝试为具有包含 EventEmitter 的依赖服务的组件编写单元测试。我已经在这个组件中订阅了这个事件发射器。我怎么能嘲笑这个呢？

相关服务：

Service A {
  testEmitter : EventEmitter<any>();
}

组件具有以下功能：

funcA() {
  service.testEmitter.subscribe()....//
}

我如何模拟此订阅？该函数在初始化期间被调用，因此测试将不起作用

Answer 1

@Injectable()
class SomeService {
  testEmitter = new EventEmitter<any>();
}

@Component({
  selector: 'app-some',
  template: ''
})
class SomeComponent implements OnInit {
  shouldCall = true;

  constructor(private someService: SomeService) {
  }

  ngOnInit() {
    if (this.shouldCall) {
      this.funcA();
    }
  }

  private funcA() {
    this.someService.testEmitter.subscribe();
  }
}

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

  beforeEach(async(() => {
    someServiceMock = {testEmitter: {subscribe: createSpy('testEmitter subscribe')}};

    TestBed.configureTestingModule({
      declarations: [SomeComponent],
      providers: [{provide: SomeService, useValue: someServiceMock}]
    }).compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(SomeComponent);
    component = fixture.componentInstance;
    // fixture.detectChanges(); // move to test suites as it cause ngOnInit call
  });

  it('should subscribe', () => {
    fixture.detectChanges();

    expect(someServiceMock.testEmitter.subscribe).toHaveBeenCalled();
  });

  it('should not subscribe', () => {
    component.shouldCall = false;

    fixture.detectChanges();

    expect(someServiceMock.testEmitter.subscribe).toHaveBeenCalled();
  });
});