使用 Jasmine 监视 Observable 订阅的结果

Question

我是 Jasmine 单元测试一个角度组件，它使用 Observables。我的组件有我正在测试的这个生命周期钩子：

ngOnInit() {
  this.dataService.getCellOEE(this.cell).subscribe(value => this.updateChart(value));
}

我有一个测试可以确保 getCellOEE 已被调用，但现在我想检查当 observable 使用新值解析时是否调用了 updateChart。这是我目前所拥有的：

let fakeCellService = {
  getCellOEE: function (value): Observable<Array<IOee>> {
    return Observable.of([{ time: moment(), val: 67 }, { time: moment(), val: 78 }]);
  }
};

describe('Oee24Component', () => {
  let component: Oee24Component;
  let service: CellService;
  let injector: Injector;
  let fixture: ComponentFixture<Oee24Component>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [Oee24Component],
      providers: [{ provide: CellService, useValue: fakeCellService }]
    })
      .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(Oee24Component);
    component = fixture.componentInstance;
    injector = getTestBed();
    service = injector.get(CellService)
    fixture.detectChanges();
    spyOn(service, 'getCellOEE').and.returnValue({ subscribe: () => { } });
    spyOn(component, 'updateChart');
  });

  it('should get cell oee on init', () => {
    component.ngOnInit();
    expect(service.getCellOEE).toHaveBeenCalled();
  });

  it('should update chart on new data', () => {
    component.ngOnInit();
    expect(component.updateChart).toHaveBeenCalled();
  });
});

但是，我得到了错误：

chrome 56.0.2924 (Windows 10 0.0.0) Oee24Component 应该在新数据上更新图表失败

预期的间谍 updateChart 已被调用。

大概这是一个时间问题，因为在测试检查时观察到的不一定解决？如果是这种情况，我该如何正确设置？

更新：

这是我的组件：

@Component({
  selector: 'app-oee24',
  templateUrl: './oee24.component.html',
  styleUrls: ['./oee24.component.css']
})
export class Oee24Component implements OnInit {
  public barChartData: any[] = [{ data: [], label: 'OEE' }];

  constructor(public dataService: CellService) { }

  ngOnInit() {
    this.dataService.getCellOEE(this.cell).subscribe(value => this.updateChart(value));
  }

  updateChart(data: Array<IOee>) {
    this.barChartData[0].data = data.map(val => val.val);
  }
}
 

Answer 1

你有没有想出一个解决方案？使用jasmine-marbles 包和complete 事件怎么样？

it('should update chart on new data', () => {
    const obs$ = cold('--a-|');
    spyOn(service, 'getCellOEE').and.returnValue(obs$);
    component.ngOnInit(); 
    obs$.subscribe({
        complete: () => {
            expect(component.updateChart).toHaveBeenCalledWith('a');
        }
    });
});

Answer 2

不确定这是否是最好的方法，但我已经看到它在我正在从事的项目中发挥作用。该方法基本上是获取订阅方法提供的回调函数的引用，并手动调用它以模拟观察者发出值：

it('should update chart on new data', () => {
    component.ngOnInit();

    // this is your mocked observable
    const obsObject = service.getCellOEE.calls.mostRecent().returnValue;

    // expect(obsObject.subscribe).toHaveBeenCalled() should pass

    // get the subscribe callback function you provided in your component code
    const subscribeCb = obsObject.subscribe.calls.mostRecent().args[0];

    // now manually call that callback, you can provide an argument here to mock the "value" returned by the service
    subscribeCb(); 

    expect(component.updateChart).toHaveBeenCalled();
  });

Answer 3

代替

spyOn(service, 'getCellOEE').and.returnValue({ subscribe: () => { } });

你可以试试

spyOn(service, 'getCellOEE').and.returnValue( {subscribe: (callback) => callback()});

Answer 4

fixture.detectChanges 触发 ngOnInit。因此，如果 fixture.detectChanges 被执行，则无需手动调用 ngOnInit。

to check if the method was called 是一种不好的做法。相反，检查代码执行的预期结果更可靠。

spyOn(service, 'getCellOEE').and.returnValue({ subscribe: () => { } }); 行中不需要，因为fakeCellService 已经正确地模拟了服务。

测试的代码是异步的，所以我们需要等到它被执行。 await fixture.whenStable(); 正是这样做的。

所以，结果测试：

const fakeData = [{ time: moment(), val: 67 }, { time: moment(), val: 78 }];
const expectedChartData = [67, 78];
const fakeCellService = {
  getCellOEE: function (value): Observable<Array<IOee>> {
    return Observable.of(fakeData);
  }
};

describe('Oee24Component', () => {
  let component: Oee24Component;
  let service: CellService;
  let injector: Injector;
  let fixture: ComponentFixture<Oee24Component>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [Oee24Component],
      providers: [{ provide: CellService, useValue: fakeCellService }]
    })
      .compileComponents();
  }));

  beforeEach(async () => {
    fixture = TestBed.createComponent(Oee24Component);
    component = fixture.componentInstance;
    fixture.detectChanges();
    await fixture.whenStable();
  });

  it('maps and saves value from the CellService.getCellOEE to barChartData[0].data when initialized', () => {
    expect(component.barChartData[0].data).toEqual(expectedChartData);
  });
});