如何使用Jest模拟第三方模块 [英] How to mock third party modules with Jest

问题描述

我目前已在我的测试目标中导入：

I've got current import in my test target:

import sharp from 'sharp'

并在我的同一测试目标中使用它：

and using it with in my same test target:

return sharp(local_read_file)
    .raw()
    .toBuffer()
    .then(outputBuffer => {

在我的测试中，我正在做下面的模拟功能：

In my test, I'm doing below to mock sharp functions:

jest.mock('sharp', () => {
  raw: jest.fn()
  toBuffer: jest.fn()
  then: jest.fn()
})

但我得到了：

  return (0, _sharp2.default)(local_read_file).
                             ^
TypeError: (0 , _sharp2.default) is not a function

有没有办法我们可以使用Jest模拟所有Sharp模块函数？ / p>

Is there a way we can mock all Sharp module functions using Jest with the function?

推荐答案

你需要像这样嘲笑：

jest.mock('sharp', () => () => ({
        raw: () => ({
            toBuffer: () => ({...})
        })
    })

首先你需要返回函数而不是一个对象，因为你调用 sharp（local_read_file）。此函数调用将返回一个对象，其中包含键 raw ，该对象包含另一个函数，依此类推。

First you need to return function instead of an object, cause you call sharp(local_read_file). This function call will return an object with key raw which holds another function and so on.

要测试您调用的每个函数都需要为每个函数创建一个间谍。由于你不能在最初的模拟调用中使用它，你可以先用间谍模拟它并稍后添加模拟：

To test on the every of your functions was called you need to create a spy for every of the function. As you can't to this in the initial mock call, you can mock it initially with a spy and add the mocks later on:

jest.mock('sharp', () => jest.fn())

import sharp from 'sharp' //this will import the mock

const then = jest.fn() //create mock `then` function
const toBuffer = jest.fn({()=> ({then})) //create mock for `toBuffer` function that will return the `then` function
const raw = jest.fn(()=> ({toBuffer}))//create mock for `raw` function that will return the `toBuffer` function
sharp.mockImplementation(()=> ({raw})) make `sharp` to return the `raw` function

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