Javascript 在 Jest 中测试 Promise 的最佳方式

Best Way to Test Promises in Jest

提问by Ambrose Little

Unless I'm misunderstanding something, the resolves and rejects (https://facebook.github.io/jest/docs/expect.html#resolves) won't be available until vNext. What is the recommended way now/in the meantime to test promises with Jest? Is it just putting expects in the thens and catches?

除非我误解了某些东西，否则在vNext 之前解析和拒绝（https://facebook.github.io/jest/docs/expect.html#resolves）将不可用。现在/同时使用 Jest 测试承诺的推荐方法是什么？它只是把期望放在然后和捕获中吗？

For example:

例如：

describe('Fetching', () => {
    const filters = {
        startDate: '2015-09-01'
    };
    const api = new TestApiTransport();

    it('should reject if no startdate is given', () => {
        MyService.fetch().catch(e => expect(e).toBeTruthy()); // see rejects/resolves in v20+
    });            

    it('should return expected data', () => {
        MyService.fetch(filters, null, api).then(serviceObjects => {
            expect(serviceObjects).toHaveLength(2);
        }).catch(e => console.log(e));
    });            
});

UPDATE 15 June 2019: Not too long after I posted this question, Jest started supporting this out of the box. I changed the accepted answer below to reflect the currently best way to do this.

2019 年 6 月 15 日更新：在我发布此问题后不久，Jest 就开始支持此问题。我更改了下面接受的答案以反映当前执行此操作的最佳方法。

回答by Yevhenii Herasymchuk

Nowadays you can write it in this way as well: docs

现在你也可以这样写：docs

describe('Fetching', () => {
    const filters = {
        startDate: '2015-09-01'
    };
    const api = new TestApiTransport(); 

 it('should reject if no startdate is given', () => {
   expect.assertions(1);
   return expect(MyService.fetch()).rejects.toEqual({
     error: 'Your code message',
   });
 });          


 it('should return expected data', () => {
   expect.assertions(1);
   return expect(MyService.fetch(filters, null, api)).resolves.toEqual(extectedObjectFromApi);
 });            
});

Update (06.01.2019)

更新 (06.01.2019)

Agree that the accepted answer doesn't work correctly as line expect.assertions(1);does all the magic. Link to docs

同意接受的答案无法正常工作，因为 line expect.assertions(1);具有所有魔力。链接到文档

expect.assertions(number) verifies that a certain number of assertions are called during a test. This is often useful when testing asynchronous code, in order to make sure that assertions in a callback actually got called.

expect.assertions(number) 验证在测试期间调用了一定数量的断言。这在测试异步代码时通常很有用，以确保回调中的断言确实被调用。

So putting this line at the top will control that the specific numberof assertions are made by the time when the test is run.

因此，将这一行放在顶部将控制在运行测试时做出的特定断言数量。

回答by Andreas K?berle

Either return a promise and expect in the resolveor catch

要么返回承诺并期望在resolve或catch

describe('Fetching', () = > {
  const filters = {
    startDate: '2015-09-01'
  };
  const api = new TestApiTransport();
  it('should reject if no startdate is given', () = > {
    return MyService.fetch()
      .catch (e => expect(e).toBeTruthy()); // see rejects/resolves in v20+
  });
  it('should return expected data', () = > {
    return MyService.fetch(filters, null, api)
      .then(serviceObjects => {
        expect(serviceObjects).toHaveLength(2);
      })
  });
});

or using async/await

或使用 async/await

describe('Fetching', () = > {
  const filters = {
    startDate: '2015-09-01'
  };
  const api = new TestApiTransport();
  it('should reject if no startdate is given', async() = > {
    try {
      const r = await MyService.fetch()
    } catch (e) {
      expect(e).toBeTruthy()
    }
  });
  it('should return expected data', async() = > {
    const serviceObjects = await MyService.fetch(filters, null, api)
    expect(serviceObjects).toHaveLength(2);
  });
});

回答by Sagan

I was able to test JEST with AXIOS for HTTP REST calls like this.

我能够使用 AXIOS 测试 JEST 以进行这样的 HTTP REST 调用。

it('has an API worth testing', async () => {
  let httpResult = null;
  await callThefunctionThatReturnsPromiseToMakeTheAxiosApiCall()
    .then(function(result) {httpResult=result;})
    .catch(function(err) {httpResult=err;});
  expect(httpResult.data.myData).toBe("myExpectedValue");
});

or

或者

it('has an API worth testing', async () => {
  let httpResult = await callThefunctionThatReturnsPromiseToMakeTheAxiosApiCall();
  expect(httpResult.data.myData).toBe("myExpectedValue");
});