在Jest中测试承诺的最佳方法 [英] Best Way to Test Promises in Jest

问题描述

除非我误会了某些内容，否则将解决并拒绝( https://facebook.github.io/jest/docs/expect.html#resolves )直到vNext才可用.现在/与此同时用Jest测试诺言的推荐方式是什么?只是把期望放在当下并抓住了吗?

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));
    });            
});

更新2019年6月15日:在我发布此问题后不久，Jest开始提供开箱即用的支持.我更改了下面的可接受答案，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.

推荐答案

如今，您也可以用这种方式编写它:

Nowadays you can write it in this way as well: 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);
 });            
});

更新(06.01.2019)

同意接受的答案不能正确地作为行 expect.assertions(1);发挥了所有魔力. 链接到文档

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

expect.assertions(number)验证是否有一定数量的断言 在测试期间被调用.这在测试时通常很有用 异步代码，以确保回调中的断言 真的被打了.

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，将此行放在顶部将控制在测试运行时做出特定的数量个断言.

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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