在 Jest 中测试 Promise 的最佳方式 [英] Best Way to Test Promises in Jest

问题描述

除非我误解了什么，否则解决和拒绝(https://facebook.github.io/jest/docs/expect.html#resolves) 在 vNext 之前不可用.现在/同时使用 Jest 测试承诺的推荐方法是什么?只是把期望放在然后和捕获中吗?

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?

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));
    });            
});

2019 年 6 月 15 日更新:在我发布这个问题后不久，Jest 就开始支持这个问题了.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.

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.

2021 年 12 月 8 日更新:在某个时候，Jest 开始支持 async/await.因此，虽然其他方法注意到了工作，但我已经(在大多数情况下)简单地使用以下内容:

UPDATE 8 Dec 2021: At some point Jest started supporting async/await. So while other methods noted work, I've taken to simply (for most cases) using something like:

it('should do something', async () => {
    const expected = true; 
    expect(await funcToTest()).toEqual(expected);
});

与大多数情况一样，async/await 比替代方案更具可读性.我现在使用 resolves 或 rejects 的唯一情况是针对简单的情况，例如:

As with most cases, async/await is much more readable than alternatives. The only case I use resolves or rejects now is for simple cases like:

it('should not throw when doing something', async () => {
    await expect(funcToTest()).resolves.not.toThrow();
});

it('should throw when something is wrong', async () => {
    await expect(funcToTest()).rejects.toThrow();
});

推荐答案

现在你也可以这样写:文档

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);
 });            
});

更新 (06.01.2019)

同意接受的答案不能正常工作expect.assertions(1); 完成了所有的魔法.文档链接

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

expect.assertions(number) 验证一定数量的断言在测试期间调用.这在测试时通常很有用异步代码，以确保回调中的断言实际上被调用了.

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.

因此将这一行放在顶部将控制在测试运行时做出特定的数量断言.

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

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