How do I deal with localStorage in jest tests?

Question

I keep getting \"localStorage is not defined\" in Jest tests which makes sense but what are my options? Hitting brick walls.

Answer 1

Currently (Oct '19) localStorage can not be mocked or spied on by jest as you usually would, and as outlined in the create-react-app docs. This is due to changes made in jsdom. You can read about it in the jest and jsdom issue trackers.

As a workaround, you can spy on the prototype instead:

// does not work:
jest.spyOn(localStorage, "setItem");
localStorage.setItem = jest.fn();

// works:
jest.spyOn(window.localStorage.__proto__, 'setItem');
window.localStorage.__proto__.setItem = jest.fn();

// assertions as usual:
expect(localStorage.setItem).toHaveBeenCalled();