如何测试Promise然后方法

Question

如何在Promise的then（）方法中测试代码。 我的代码的then（..）方法内部没有看到代码的代码覆盖率。 我的单元测试通过并没有引发任何错误，但是当我查看行覆盖率时，toPromise.then（//此代码）内部的代码未覆盖。 我如何测试该代码。

//service file
getDataFromAPI(num: string): Promise<Model> {
  return this._http
   .get<Model>('url')
   .toPromise()
   .then(resolve => {
       const { item1, item2, item3 } = resolve;
       return { item1, item2, item3 };
  });
}


//unit test
describe('getDataFromAPI', () => {
it('should get data', () => {

  const service: Service = TestBed.get(Service);
  const httpClientGetSpy = jest.spyOn(httpClient, 'get');

  service.getDataFromAPI(num).then(response => {
    expect(response.item1).toEqual('one');
    expect(response.item2).toEqual('two');
    expect(response.item3).toEqual('three');
  });

  expect(httpClientGetSpy).toHaveBeenCalled();
});
});

Answer 1

那是因为异步任务。 承诺之前，您的测试结束，以便then回调永远不会被调用。

只需更改测试以处理async

方法1

使用fakeAsync提供的fakeAsync ： https : fakeAsync

it('should get data', fakeAsync(() => {

  const service: Service = TestBed.get(Service);
  const httpClientGetSpy = jest.spyOn(httpClient, 'get');

  service.getDataFromAPI(num).then(response => {
    expect(response.item1).toEqual('one');
    expect(response.item2).toEqual('two');
    expect(response.item3).toEqual('three');
  });

  expect(httpClientGetSpy).toHaveBeenCalled();
}));

方法2

从ES2016开始使用async/await ： https : //developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/await

it('should get data', async() => {

  const service: Service = TestBed.get(Service);
  const httpClientGetSpy = jest.spyOn(httpClient, 'get');

  let response = await service.getDataFromAPI(num);
  expect(response.item1).toEqual('one');
  expect(response.item2).toEqual('two');
  expect(response.item3).toEqual('three');

  expect(httpClientGetSpy).toHaveBeenCalled();
});

方法3

处理何时应以done功能结束测试：

it('should get data', (done) => {

  const service: Service = TestBed.get(Service);
  const httpClientGetSpy = jest.spyOn(httpClient, 'get');

  service.getDataFromAPI(num).then(response => {
    expect(response.item1).toEqual('one');
    expect(response.item2).toEqual('two');
    expect(response.item3).toEqual('three');
    done();
  });

  expect(httpClientGetSpy).toHaveBeenCalled();
});