测试从服务返回的承诺解析

Question

我在测试函数返回的 promise 的 promise 解析时遇到了问题。问题是 .then() 没有被执行。

我正在测试的组件方法：

 private _openToast(): void {
        this._toast
            .action()
            .then(
                () => {
                    this.test();
                },
                () => {}
            );
    }
    
test(): void {
console.log("It's ok")
}

服务

@Injectable()
export class ToastService {
    constructor(private _toast: OuterToastService) {}

    action<ValueType>(context?: Partial<IToastContext>, config?: Partial<ToastConfig>): Promise<ValueType> {
        return this._toast.open(); // It's material-like toast service that returns promise
    }
}

并测试

describe('Component', () => {
    let component: Component;
    let fixture: ComponentFixture<Component>;
    const MockToastService = jasmine.createSpyObj('toast', ['action']);
    beforeEach(() => {
        TestBed.configureTestingModule({
            declarations: [Component],
            providers: [
                { provide: ToastService, useValue: MockToastService },
            ],
        });

        fixture = TestBed.createComponent(Component);
        component = fixture.componentInstance;
    });
    })

it('should call test() if toast accepted', () => {
            MockToastService.action.and.returnValue(Promise.resolve());
            const spy = spyOn<any>(component, 'test');

            component['_openToast']();
            expect(spy).toHaveBeenCalled();
        });

运行测试的结果是： Expected spy test to have been called. 这意味着（我相信如此） .then() 没有被执行。为什么？

Answer 1

Which means (I believe so) that .then() isn't executed. Why?

您的测试是完全同步的，因此没有时间调用 this.test()。由 MockToastService 编辑的承诺 return 可能处于已解决状态，但 .then 回调仍然是异步的运行s，下一次微任务是运行.

要解决此问题，您需要使 openToast return 成为一个承诺，然后让您的测试等待该承诺：

private _openToast(): void {
  return this._toast.action().then(
    () => {
      this.test();
    },
    () => {}
  );
}

it("should call test() if toast accepted", () => {
  MockToastService.action.and.returnValue(Promise.resolve());
  const spy = spyOn<any>(component, "test");

  return component["_openToast"]().then(() => {
    expect(spy).toHaveBeenCalled();
  });
});

或者，您可以使用 fakeAsync 测试，然后强制刷新微任务队列：

import { fakeAsync, flushMicrotasks } from '@angular/core/testing';

it("should call test() if toast accepted", fakeAsync(() => {
  MockToastService.action.and.returnValue(Promise.resolve());
  const spy = spyOn<any>(component, "test");

  component["_openToast"]();

  flushMicrotasks();

  expect(spy).toHaveBeenCalled();
}));

测试从服务返回的承诺解析

Testing promise resolving returned from service

angular

jasmine

karma-jasmine