mock local storage in jest

Question

I'm trying to mock local storage but keep getting an error.

Matcher error: received value must be a mock or spy function

const sessionStorageMock = {
  getItem: jest.fn(),
  setItem: jest.fn(),
};

global.sessionStorage = sessionStorageMock;

test('expect', () => {
  mySessionSetFunction();
  expect(sessionStorage.setItem).toHaveBeenCalled();
});

I even tried.

  const spy = jest.spyOn(sessionStorage, 'setItem');
  expect(spy).toHaveBeenCalled();

but it never gets called.

Look on https://stackoverflow.com/questions/32911630/how-do-i-deal-with-localstorage-in-jest-tests — begin29, Mar 18 '19 at 19:05
Yes saw that but it doesn't work. expect(localStorage.getItem).toBeCalledWith('token') — me-me, Mar 18 '19 at 19:11
will `mySessionSetFunction()` creates `token` key within local storage? — begin29, Mar 18 '19 at 19:27
mySessionSetFunction() is just running through an object of keys and setting sessionStorage.setItem(key, value); — me-me, Mar 18 '19 at 19:31
This worked for me. jest.spyOn(Storage.prototype, 'setItem'); Thanks for the help Vadym Motsukh — me-me, Mar 18 '19 at 19:47

score 0 · Answer 1 · answered Sep 09 '19 at 16:04

Here is a solution:

function mySessionSetFunction() {
  sessionStorage.setItem('name', 'jest');
}

export { mySessionSetFunction };

Unit test:

/**
 * @jest-environment jsdom
 */
import { mySessionSetFunction } from './';

const sessionStorageBackup = (global as any).sessionStorage;

delete (global as any).sessionStorage;
(global as any).sessionStorage = {
  setItem: jest.fn()
};

describe('test suites', () => {
  afterAll(() => {
    (global as any).sessionStorage = sessionStorageBackup;
  });
  it('t1', () => {
    mySessionSetFunction();
    expect((global as any).sessionStorage.setItem).toBeCalledWith('name', 'jest');
    expect(jest.isMockFunction((global as any).sessionStorage.setItem)).toBeTruthy();
  });
});

Here is the completed demo: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/55228389

mock local storage in jest

1 Answers1