How to mock an exported const in jest

Question

I have a file that relies on an exported const variable. This variable is set to true but if ever needed can be set to false manually

Answer 1

Facing the same issue, I found this blog post very useful, and much simpler than @cyberwombat use case :

https://remarkablemark.org/blog/2018/06/28/jest-mock-default-named-export/

// esModule.js
export default 'defaultExport';
export const namedExport = () => {};

// esModule.test.js
jest.mock('./esModule', () => ({
  __esModule: true, // this property makes it work
  default: 'mockedDefaultExport',
  namedExport: jest.fn(),
}));

import defaultExport, { namedExport } from './esModule';
defaultExport; // 'mockedDefaultExport'
namedExport; // mock function

Answer 2

I solved this by initializing constants from ContstantsFile.js in reducers. And placed it in redux store. As jest.mock was not able to mock the contstantsFile.js

constantsFile.js
-----------------
const MY_CONSTANTS = {
MY_CONSTANT1: "TEST",
MY_CONSTANT2: "BEST",
};
export defualt MY_CONSTANTS;

reducers/index.js
-----------------
import MY_CONST from "./constantsFile";

const initialState = {
...MY_CONST
}
export const AbcReducer = (state = initialState, action) => {.....}

ABC.jsx
------------
import { useSelector } from 'react-redux';
const ABC = () => {
const const1 = useSelector(state) => state. AbcReducer. MY_CONSTANT1:
const const2 = useSelector(state) => state. AbcReducer. MY_CONSTANT2:
.......

Now we can easily mock the store in test.jsx and provide the values to constant that we want.

Abc.text.jsx
-------------
import thunk from 'redux-thunk';
import configureMockStore from 'redux-mock-store';

describe('Abc mock constants in jest', () => {
const mockStore = configureMockStore([thunk]);
let store = mockStore({
   AbcReducer: {
      MY_CONSTANT1 ="MOCKTEST",
      MY_CONSTANT2 = "MOCKBEST",
   }
});

test('your test here', () => { .....

Now when the test runs it will always pick the constant value form mock store.