mock lodash debounce in jest

test.js

// somewhere on top
import _ from 'lodash';
jest.unmock('lodash');

// then
_.debounce = jest.fn((fn) => fn);

can you explain why this works? If I don't do that, I receive "Expected a function" error

Because you're replacing the actual bottom line implementation, so in your tests when you call debounce it will try calling a function on an undefined variable.

import debouce
    from 'lodash/debounce';

// Tell jest to mock this import
jest.mock('lodash/debounce');

// Assign the import a new implementation, in this case it's execute the function given to you
debouce.mockImplementation(fn => fn);

This is great! What if I also want to mock the cancel method that is returned on the debounce instance?

Maybe someone else finds it useful, but what worked for me is adding jest.mock('lodash.debounce', () => jest.fn(fn => fn)) to jest setup file

You have to call the function and ignore the timer jest.mock('lodash/fp/debounce', () =>jest.fn((nr, fn) => fn())). This worked for me.

This is great! What if I also want to mock the cancel method that is returned on the debounce instance?

@smanwaring I've managed to mock cancel like this:

import debounce from "lodash/debounce";

jest.mock("lodash/debounce", () =>
  jest.fn(fn => {
    fn.cancel = jest.fn();
    return fn;
  })
);

This worked for me

jest.mock('lodash', () => ({
...require.requireActual('lodash'), debounce: fn => {
fn.cancel = jest.fn(); return fn;
},}));`

This worked for me

jest.mock('lodash', () => ({ ...require.requireActual('lodash'), debounce: fn => { fn.cancel = jest.fn(); return fn; }, }));

Yep this is the one that finally sorted it for me too. Thanks a lot.

Since require.requireActual was removed in Jest v26 (jestjs/jest#9854), I believe you should use jest.requireActual

It all depends how you import debounce

for
import { debounce } from 'lodash'

add to the top of your test (after imports)

const lodash = require('lodash')
lodash.debounce = jest.fn(fn => fn)

for
import debounce from 'lodash/debounce';
use
jest.mock('lodash/debounce', () => jest.fn(fn => fn));

Thanks so much @qweluke. How hard it is to find this information.

jest.mock('lodash', () => {
  const module = jest.requireActual('lodash');
  module.debounce = jest.fn(fn => fn);
  return module;
});

You have to call the function and ignore the timer jest.mock('lodash/fp/debounce', () =>jest.fn((nr, fn) => fn())). This worked for me.

Thank you so much, this worked for me.

jest.mock('lodash.debounce', () => jest.fn(fn => fn))

This works , Thanks

This worked for me wonderfully

jest.mock('lodash', () => ({
...require.requireActual('lodash'), debounce: fn => {
fn.cancel = jest.fn(); return fn;
},}));`

Thanks.

Updated version of @mos-adebayo's above that worked for me (using lodash-es)

jest.mock('lodash-es', () => ({
  ...jest.requireActual('lodash-es'),
  debounce: (fn) => {
    fn.cancel = jest.fn();
    return fn;
  },
}));

You have to call the function and ignore the timer jest.mock('lodash/fp/debounce', () =>jest.fn((nr, fn) => fn())). This worked for me.

👍

This worked for me perfectly:

import * as lodash from 'lodash-es';
// other imports...

jest.mock('lodash-es/debounce', () => ({
  default: jest.fn(fn => fn),
  __esModule: true
}));

// describe block...