如何使捕获的承诺在开玩笑中失败 [英] How to make catched promises fail in jest

问题描述

考虑这个功能：

aPromise = require('axios');    
function middleware(callback) {
  axios.get('/api/get')
    .then(callback)
    .catch(callback);
}

考虑这个测试：

const callback = (err) => {
  expect(isError(err)).toBe(true);
  done();
};

middleware(callback);

isError 是一个lodash功能。

The isError is a lodash function.

考虑 aPromise 作为我想要测试的东西。如果承诺总是解决，那么这个测试不应该通过。但它会！那是因为承诺的捕获实际上捕获了期望异常。

Consider aPromise as something I want to test. If the promise always resolves, this test should not pass. But it will! And that's because the promise's catch actually catches the expect exception.

我的问题是：如何捕获错误在承诺的 catch 处理程序时 expect 在promise的中抛出错误然后 handler？

My question is: How to not catch the error in a promise's catch handler when expect throws an error in the promise's then handler?

请注意，我不使用async / await。

Note that I don't use async/await.

推荐答案

您需要创建失败的承诺，并且需要在测试中返回承诺。请查看测试承诺的文档。

You need to create a failed promise and you need to return the promise in your test. Please have a look on the doc on testing promises.

aPromise = require('axios');    
jest.mock('axios', () => {
  get: ()=> jest.fn() //initialy mock the get function
})

it('catch failing promises',() = > {
    const result  = Promise.reject('someError'); //create a rejected promises
    aPromise.get.mockImplementation(() => result)// let `get` return the rejected promise
    const callback = jest.fn()
    middleware(callback)

    return result
        .then (()=>{
          expect(callback).toHaveBeenCalledWith('someError');
        })

})

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