while running  __tests__/infiniteTimerGame-test.js, i got following error:

expect(received).toHaveBeenCalledTimes(expected)

    Matcher error: received value must be a mock or spy function

    Received has type:  function
    Received has value: [Function setTimeout]

      12 |     // At this point in time, there should have been a single call to
      13 |     // setTimeout to schedule the end of the game in 1 second.
    > 14 |     expect(setTimeout).toHaveBeenCalledTimes(1);
         |                        ^
      15 |     expect(setTimeout).toHaveBeenLastCalledWith(expect.any(Function), 1000);

so i added, jest.spyOn(global, 'setTimeout');