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

我的测试目标中有当前导入:

I've got current import in my test target:

import sharp from 'sharp'

并在我的同一个测试目标中使用它:

and using it with in my same test target:

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

在我的测试中，我在下面模拟了尖锐的函数:

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:

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

有没有办法使用 Jest 和函数来模拟所有 Sharp 模块函数?

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

推荐答案

你需要像这样模拟它:

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

首先你需要返回函数而不是对象，因为你调用了sharp(local_read_file).此函数调用将返回一个键为 raw 的对象，该对象包含另一个函数等等.

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，您需要为每个函数创建一个间谍.由于您无法在初始模拟调用中进行此操作，因此您可以先使用间谍对其进行模拟，然后再添加模拟:

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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