Import function from a Jest manual mock with Typescript

Question

I\'m creating a custom mock (of an ES6 class) with Jest in a Typescript project. The mock creates end exports a few mock.fn() so that they could be spied on in

Answer 1

I have the same problem and I only have a workaround. My problem is that I manually mock fs from node.

So I have a manual mock for 'fs' which looks roughly like this:

const fs = jest.genMockFromModule("fs");

let mockFiles = {};

function __clearMocks(){
    mockFiles = {};
}

module.exports = fs;

So clearly when my test case imports fs it would not work:

import * as fs from 'fs';
fs.__clearMocks();

To get this working I create an extension of the type:

declare module 'fs' {
    export function __clearMocks(): void; 
}

So now I can modify my testcase like this:

import * as fs from 'fs';
import 'fsExtension';
fs.__clearMocks();

Hopefully this helps you!

Answer 2

The easiest way to fix this is to use ts-jest's mocked() helper. The helper will make sure you have access to the mock test methods. __tests__/soundPlayer.ts would then look as follows:

// __tests__/soundPlayer.ts
import { mocked } from "ts-jest/utils";
import SoundPlayer from '../soundPlayer';

jest.mock('../soundPlayer');

const soundPlayer = mocked(new SoundPlayer());

beforeEach(() => {
  soundPlayer.playSoundFile.mockClear();
});

it('is called with filename', () => {
  const filename = 'song.mp3';

  soundPlayer.playSoundFile(filename);

  expect(soundPlayer.playSoundFile).toBeCalledWith(filename);
});

If you really want to include mockPlaySoundFile you could do it by telling the Typescript compiler to suppresses the import error:

// @ts-ignore
import { mockPlaySoundFile } from '../soundPlayer';

Also, have a look at the example in my repo here: https://github.com/tbinna/ts-jest-mock-examples, in particular, your soundPlayer example: https://github.com/tbinna/ts-jest-mock-examples/tree/master/sound-player