Cook

Mocking a named import

import { getTime } from './time';

jest.mock('./time', () => ({
  getTime: () => '1:11PM',
}));

Mocking only the named import (and leaving other imports unmocked)

import { getTime, isMorning } from './time';

jest.mock('./time', () => ({
  ...jest.requireActual('./time'), 
  getTime: () => '1:11PM',
  // isMorning will return its true value
}));

Mocking a default import

import getDayOfWeek from './time';

jest.mock('./time', () => () => 'Monday');

Mocking default and named imports

If you want to mock default and named imports, you’ll need to remember to use __esModule: true

import getDayOfWeek, { getTime } from './time';

jest.mock('./time', () => ({
  __esModule: true,
  default: () => 'Thursday'
  getTime: () => '1:11PM',
}));

Changing what the mock returns per test

If you wanted to have getDayOfWeek to return a different value per test, you can use mockReturnValue in each of your tests

• If you only wanted to change what the mocked function returned for just one test, you need to use mockReturnValueOnce, otherwise you will change the mock for all other subsequent tests.

import getDayOfWeek from './time';
jest.mock('./time', () => jest.fn());

test('App renders Monday', () => {
  getDayOfWeek.mockReturnValue('Monday');
});

Mocking Third Party library (e.g. Axios)

import * as axios from 'axios'

jest.mock('axios')

test('good response', () => {
  axios.get.mockResolvedValue({ status: 200, data: {...} })
})
test("bad response", () => {
  axios.get.mockRejectedValue({ ... });
})