试图期望使用 JEST 调用匿名函数中的函数

Question

I'm trying to test that a call to console.warn has been made :

Function :

trackError({ eventCategory, eventAction, eventLabel, errorResponse = false }) {
    if (typeof window.ga !== 'undefined') {
        window.ga('send', 'event', eventCategory, eventAction, eventLabel, {
            hitCallback: () => {
                if (errorResponse) {
                    console.warn(eventLabel + ' :: errorResponse => ', errorResponse)
                } else {
                    console.warn(eventLabel)
                }
            }
        })
    }
}

Test:

it('should emit a console.warn with the eventLabel variable only', () => {
    window.ga = jest.fn()
    console.warn = jest.fn()

    trackError({
        eventCategory: 'PMC',
        eventAction: 'error',
        eventLabel: 'not found'
    })

    expect(window.ga).toHaveBeenCalledWith('send', 'event', 'PMC', 'error', 'not found', {
        hitCallback: expect.any(Function)
    })
    // expect(window.ga).toHaveBeenCalledWith('send', 'event', 'PMC', 'error', 'not found', {
    // hitCallback: jest.fn().mockImplementationOnce(() => {
    //         expect(console.warn).toHaveBeenCalledWith('not found')
    //     })
    // })
})

Answer 1

Rather than manually overwriting each of the functions with a jest.fn() , you probably want to use jest.spyOn() instead, since it allows you to restore the initial functions after the test by calling mockFn.mockRestore() .

The main issue is that you need to mock the window.ga() implementation to synchronously invoke your hitCallback() .

it('should emit a console.warn with the eventLabel variable only', () => {
  const ga = jest.spyOn(window, 'ga').mockImplementation(
    (command, hitType, eventCategory, eventAction, eventLabel, { hitCallback }) => {
      hitCallback();
    }
  );
  const warn = jest.spyOn(console, 'warn').mockImplementation(
    () => {}
  );

  trackError({
    eventCategory: 'PMC',
    eventAction: 'error',
    eventLabel: 'not found'
  });

  expect(ga).toHaveBeenCalledWith('send', 'event', 'PMC', 'error', 'not found', {
    hitCallback: expect.any(Function)
  });

  expect(warn).toHaveBeenCalledWith('not found');

  ga.mockRestore();
  warn.mockRestore();
});