Jest mock localStorage methods

Question

I would like to mock localStorage methods in jest for error simulation. I have localstorage getter and setter methods defined in utility.js. I would like to mock local

Answer 1

If you want to test localStorage functions then I would like to suggest the jest-localstorage-mock npm package.

After configuring this package in your setup test file as per documentation, then you could do this after.

test('should save to localStorage', () => {
  const KEY = 'foo',
    VALUE = 'bar';
  dispatch(action.update(KEY, VALUE));
  expect(localStorage.setItem).toHaveBeenLastCalledWith(KEY, VALUE);
  expect(localStorage.__STORE__[KEY]).toBe(VALUE);
  expect(Object.keys(localStorage.__STORE__).length).toBe(1);
});


test('should have cleared the sessionStorage', () => {
  dispatch(action.reset());
  expect(sessionStorage.clear).toHaveBeenCalledTimes(1);
  expect(sessionStorage.__STORE__).toEqual({}); // check store values
  expect(sessionStorage.length).toBe(0); // or check length
});