Discussion on: Testing React Hook State Changes

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Replies for: Yup, so the issue is because we are spying on React.useState, which sets a spy on the default export from 'react'. Since you are pulling in useStat...

Great, thanks. I'll play around with it - we're using useState as a named export all over the place - wouldn't be a HUGE deal to convert but it'd be nice to figure out how to test as-is.

Kit Randel • Oct 1 '19

Did you happen to find a solution?

Piotr • Nov 25 '19

to make it work with useState we would have to mock it using jest while keeping rest of react intact. jest.requireActual can be used to achieve that

import React, { useState as useStateMock } from 'react';

jest.mock('react', () => ({
  ...jest.requireActual('react'),
  useState: jest.fn(),
}));

describe('Test', () => {
  const setState = jest.fn();

  beforeEach(() => {
    useStateMock.mockImplementation(init => [init, setState]);
  });

...

Jonah Bolotin • Feb 22 '20

The following technique works well for me testing functional components with useState destructured. This is an adapted solution from that above because the mockImplementation above caused react-test-renderer tests to fail:

import * as React from 'react';

describe('Some message', () => {
    const setState = jest.fn();
    // eslint-disable-next-line @typescript-eslint/no-explicit-any
    const useStateMock: any = (initState: any) => [initState, setState];

    afterEach(() => {
      jest.clearAllMocks();
    });

    it('Is a test where we want to mock useState', () => {
          jest.spyOn(React, 'useState').mockImplementation(useStateMock);
          const wrapper = shallow(<Component {...props} />);
          // trigger setState somehow
          expect(setState).toHaveBeenCalledTimes(1);
          // Other tests here
    });
});

This is typescript, but it should work just as well in JS if you remove the type annotations