在 Angular 的 onInit() 中为订阅编写单元测试

Question

我有一个如下所示的 Spinner 组件类，它将使用 Angular 材料显示/隐藏 Progress Spinner。

export class SpinnerComponent implements OnInit, OnDestroy {
    visible = true;
    private subscription: Subscription;

    constructor(private spinnerService: SpinnerService) {}

    ngOnInit() {
         this.subscription = this.spinnerService.spinnerState.subscribe((state: SpinnerState) => {
                this.visible = state.show;
           });
     }
    ngOnDestroy() {
         if (this.subscription) {
            this.subscription.unsubscribe();
         }
    }
}

如何编写一个规范来测试下面显示的特定行，该行位于 ngOnInit() 方法中？

this.visible = state.show;

Answer 1

第一个解决方案：

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { SpinnerComponent } from './spinner.component';
import { of } from 'rxjs/observable/of';

describe('SpinnerComponent', () => {
  let component: SpinnerComponent;
  let fixture: ComponentFixture<SpinnerComponent>;
  const fakeSpinner = {
    spinnerState: of({ show: false }),
  };

  beforeEach(
    async(() => {
      TestBed.configureTestingModule({
        declarations: [SpinnerComponent],
        providers: [{ provide: SpinnerService, useValue: fakeSpinner }],
      }).compileComponents();
    }),
  );

  beforeEach(() => {
    fixture = TestBed.createComponent(SpinnerComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should set component.visible based on spinnerService state', () => {
    expect(component.visible).toEqual(false)
  });
});

需要注意的重要一点是，我们提供的是 spinner 服务的模拟实现。

第二种解决方案：

另一种测试方法是创建一个浅层测试，根本不使用 Angular 测试实用程序。由于您不关心模板交互，因此您也可以像测试常规 ts 类一样对其进行测试。

class FakeSpinnerService {
  private spinnerStateSource = new Subject();
  spinnerState = this.spinnerStateSource.asObservable();

  emit(val: boolean) {
    this.spinnerStateSource.next({ show: val });
  }
}

it('should set component.visible based on spinnerService state', () => {
  const fakeService = new FakeSpinnerService();
  const component = new SpinnerComponent(fakeService as any);

  // initial value
  expect(component.visible).toBe(true);

  component.ngOnInit();

  fakeService.emit(false);
  expect(component.visible).toBe(false);

  fakeService.emit(true);
  expect(component.visible).toBe(true);
});