为什么我的异步角度茉莉花单元测试不起作用？

Question

我正在尝试测试异步组件方法，我认为我正确使用了 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，它不会等待承诺解决。函数的异步性质似乎导致超时被触发并且测试过早退出。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() 包装器函数并切换到传入 done 回调并在 whenStable() 块末尾调用它的 Jasmine 语法，它可以正常工作。谁能告诉我为什么它不适用于 Angular async() 包装器？

我的代码如下所示：

// 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的beforeEach()方法中的调用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();
});

Answer 2

我在处理这个问题时遇到了一些麻烦，我们通过使用 beforeEach 中的角度/测试异步函数解决了它：

beforeEach(async(() => { // <-- use async
    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();
}));

。正如文档所说：https://angular.io/guide/testing#async-test-with-async。