JS/Jest: mocking a class to check if method called

Question

I am trying to test the loading of a player in my main js file. It just created a new instance of an IVSPlayer class and then calls init() on it.
MAIN.js

const ivsPlayer = new IVSPlayer({
  id: VIDEO_PLAYER_ID,
  config: VIDEO_JS_CONFIG,
  ivsTech: win.registerIVSTech,
});
ivsPlayer.init();

player = ivsPlayer.player;

I am trying to mock the implementation below

MAIN.test.js

import IVSPlayer from './ivs-player';

it('should load the  player', async () => {
  const mockInit = () => jest.fn();

  jest.mock('./ivs-player', () => {
    return {
      init: mockInit,
    };
  });

  await createPlayers();

  expect(?????).toHaveBeenCalled();
});

What do I put in for the expect to listen to since I mocked the ivs-player

Answer 1

I think your mocking is wrong. Try this (mock on the prototype)

it('should load the  player', async () => {
  IVSPlayer.prototype.init = jest.fn().mockImplementation(() => {
    return {
      init: jest.fn(),
    };
  });

  // execute code that causes the init function to run

  expect(IVSPlayer.prototype.init).toHaveBeenCalled();
});

Alternatively, you can try this

import { IVSPlayer } from './ivs-player';

jest.mock('./ivs-player'); // Automatic mock of the file

it('should load the  player', async () => {
  // execute code that causes the init function to run

  const mockInit = IVSPlayer.mock.instances[0].init;

  expect(mockInit).toHaveBeenCalled();
});

You can read more on class mocks here .