angular - 为什么我的异步 Angular Jasmine 单元测试不工作？

Question

我正在尝试测试一个异步组件方法，并且我认为我正确地使用了 Angular 4 的异步测试功能，但它不起作用。我的问题是，当我运行测试时，它不会等待 Promise 解决。似乎函数的异步性质导致超时被触发并且测试被过早退出。无论如何，测试都会通过，因为 whenStable() 中的所有 expect() 语句都会被跳过。

如果我省略 async() 包装函数并切换到传入 done 回调的 Jasmine 语法，并在 whenStable 结束时调用它() block ，它工作正常。谁能告诉我为什么它不适用于 Angular async() 包装器？

我的代码是这样的:

// my.component.ts
ngOnInit() {
  this.getResults().then((results) => {
    this.results = results;
  });
}

// My asynchronous function, which takes 1.5s to load results
getResults() {
  let promise = new Promise((resolve) => {
    setTimeout(() => {
      resolve('foo');
    }, 1500);
  })
  return promise;
}


// my.component.spec.ts (Angular async version which doesn't work)
it('should load results', async(() => {
  spyOn(component, 'getResults').and.returnValue(Promise.resolve('bar'));
  component.ngOnInit();

  fixture.whenStable().then(() => {
    // Everything in here gets skipped when I run the test
    fixture.detectChanges();
    // This should cause the test to fail, but it doesn't because it's not run in time
    expect(true).toBe(false)
  });
}));

// my.component.spec.ts (Jasmine version that works)
it('should load results', (done) => {
  spyOn(component, 'getResults').and.returnValue(Promise.resolve('bar'));
  component.ngOnInit();

  fixture.whenStable().then(() => {
    fixture.detectChanges();
    // This should fail and it does because the test works using Jasmine's "done" callback
    expect(true).toBe(false);
    done();
  });
});

Answer 1

感谢@yurzui 的 Plunker，我确定我的问题是由我在 beforeEach() 方法中调用 fixture.detectChanges() 引起的:

beforeEach(() => {
    TestBed.configureTestingModule({
      declarations: [AppComponent],
    });

    fixture = TestBed.createComponent(AppComponent);

    component = fixture.componentInstance;

    // The following line is to blame! Removing it makes the test work correctly.
    fixture.detectChanges();
});