How to mock third party modules with Jest

Question

I've got current import in my test target:

import sharp from 'sharp'

and using it with in my same test target:

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

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

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

but I'm getting:

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

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

score 16 · Accepted Answer · edited Jan 19 '23 at 18:17

16

You need to mock it like this :

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

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.

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

edited Jan 19 '23 at 18:17

Ako

197
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13

answered Sep 11 '17 at 17:00

Andreas Köberle

106,652
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How do I now use spyon to get callcount and args on it (sharp)? Can I actually do this? `const sharpSpy = jest.spyOn("sharp", "raw") expect(sharpSpy).toBeCalled(); expect(sharpSpy.mock.calls.length).toEqual(1);` This seem to fail in my test – Passionate Engineer Sep 12 '17 at 15:27
This needs to be a bit more complicate way of mocking it. I will update my answer. – Andreas Köberle Sep 12 '17 at 19:54
I get `TypeError: (0 , _sharp2.default)(...).raw is not a function` error when I use that method by adding mocks later on. – Passionate Engineer Sep 13 '17 at 03:35
Argh, you are right it must return an object not just the function, updated my answer. – Andreas Köberle Sep 13 '17 at 06:20
I still seem to get `TypeError: Cannot read property 'raw' of undefined` any ideas why? – Passionate Engineer Sep 13 '17 at 08:59
any help would be great here – Passionate Engineer Sep 16 '17 at 02:07
1

ah, I just forgot the `()` around `{raw}` and the other returning objects. Updated the answer. – Andreas Köberle Sep 16 '17 at 11:50
thanks it works but how do I get number of times a particular mock is called then? I have something like ```test("sharp being called", () => { imageResizer.lambda_handler(records) expect(sharp).toBeCalled(); expect(sharp.raw.mock.calls.length).toEqual(1); })``` but it seems to not pick up how many times ```sharp``` has been called this is the mock ```sharp.mockImplementation(()=> ({raw}))``` – Passionate Engineer Oct 05 '17 at 10:07
any help would be great here – Passionate Engineer Oct 15 '17 at 00:29

How to mock third party modules with Jest

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