angular - 如何测试Material2 snack-bar？

Question

我有一个关于 Angular 5 的项目，我遇到了以下问题。我有一个触发显示 snackbar 的组件 ComponentWithSnackBar:

showSnackBar() {
  this.snackBar.open('Message text', 'Close', {
    duration: 5000,
    verticalPosition: 'top',
  });
}

它按预期工作。但我不知道如何测试它。我尝试编写测试:

describe('ComponentWithSnackBar', () => {
  let snackBar: MatSnackBar;
  let overlayContainer: OverlayContainer;
  let overlayContainerElement: HTMLElement;

  function createComponent<T>(component: Type<T>, providers: Provider[] = [], declarations: any[] = []): ComponentFixture<T> {
    TestBed.configureTestingModule({
      imports: [AppModule, RouterTestingModule, NoopAnimationsModule],
      declarations: declarations,
      schemas: [CUSTOM_ELEMENTS_SCHEMA],
      providers,
    }).compileComponents();

    inject([MatSnackBar, OverlayContainer], (sb: MatSnackBar, oc: OverlayContainer) => {
      snackBar = sb;
      overlayContainer = oc;
      overlayContainerElement = oc.getContainerElement();
    })();

    return TestBed.createComponent<T>(component);
  }

  it(`Should display snack-bar`, fakeAsync(() => {
    const fixture = createComponent(ComponentWithSnackBar);
    const component: ComponentWithSnackBar = fixture.debugElement.componentInstance;

    fixture.detectChanges();
    const button = fixture.debugElement.query(By.css('button')); //button which triggers method showSnackBar 
    button.triggerEventHandler('click', null);
    fixture.detectChanges();
    flush();

    const messageElement = overlayContainerElement.querySelector('snack-bar-container');
    expect(messageElement.textContent).toContain('Message text');
  }));
});

结果我得到错误

TypeError: Cannot read property 'textContent' of null

我做错了什么？感谢您的提前!

Answer 1

以下对我有用:

describe('MyComponent', () => {
  let component: MyComponent;
  let fixture: ComponentFixture<MyComponent>;
  let element: any;
  let overlayContainer: OverlayContainer;
  let overlayContainerElement: HTMLElement;
  let snackBar: MatSnackBar;

....

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

beforeEach(inject([MatSnackBar, OverlayContainer],
    (sb: MatSnackBar, oc: OverlayContainer) => {
      snackBar = sb;
      overlayContainer = oc;
      overlayContainerElement = oc.getContainerElement();
    }));

....

 it('should show my success message', () => {
      
   const containerElement = overlayContainerElement.querySelector('simple-snack-bar');
   
   expect(containerElement.textContent).toContain('My success text');
 });