Jest createSpyObj

Question

With Chai, you can create a spy object as follows:

chai.spy.object([ \'push\', \'pop\' ]);

With jasmine, you can use:

jasmi         


        

Answer 1

const video = {
  play() {
    return true;
  },
};

module.exports = video;

And the test:

const video = require('./video');

test('plays video', () => {
  const spy = jest.spyOn(video, 'play');
  const isPlaying = video.play();

  expect(spy).toHaveBeenCalled();
  expect(isPlaying).toBe(true);

  spy.mockReset();
  spy.mockRestore();
});

Docs found here: https://facebook.github.io/jest/docs/en/jest-object.html#jestspyonobject-methodname

There is also jest.fn()

const mockFn = jest.fn();
  mockFn();
  expect(mockFn).toHaveBeenCalled();

  // With a mock implementation:
  const returnsTrue = jest.fn(() => true);
  console.log(returnsTrue()); // true;

https://facebook.github.io/jest/docs/en/jest-object.html#jestfnimplementation