useFakeTimers no longer mocks out timer functions properly

[jsumnerp]

🐛 Bug Report

With the new fakeTimers the setTimeout, setInterval, clearTimeout, clearInterval functions are no longer properly mocked

● waits 1 second before ending the game

expect(received).toHaveBeenCalledTimes(expected)

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

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

To Reproduce

https://jestjs.io/docs/timer-mocks using the first example

Expected behavior

For timer functions to be mocked or docs to be updated to show how to get the same results

[LeonardDrs]

Worth noting that jest.useFakeTimers('legacy'); still works for this kind of issue for the time being.

[SimenB]

they are mocked, but they are not mock functions. This is on purpose. See #5171 (although that's not the PR that landed, it contains notes of all the differences between "modern" and "legacy" fake timers)

• Jest added spies to the fake timers automatically. We no longer do that, people need to do e.g. jest.spyOn(global, 'setTimeout') themselves.

[donaldpipowitch]

Would using jest.useFakeTimers('legacy'); really fully restore the behaviour of Jest 26? We have a couple of tests which fail on Jest 27 no matter how I rewrite them.

They look a bit like this:

beforeAll(() => {
  jest.useFakeTimers();
});

afterAll(() => {
  jest.useRealTimers();
});

test('<SomeComponent/>: just an example', async () => {
  const { findByText, getByTestId, queryByText } = render(<SomeComponent />);

  expect(queryByText('...')).not.toBeInTheDocument();

  fireEvent.click(getByTestId('...'));
  act(() => {
    jest.advanceTimersByTime(5000);
  });

  expect(await findByText('...')).toBeInTheDocument();
});

[SimenB]

Both timer systems are the same as in Jest 26, we've just flipped the default implementation

[kenlyon]

Since this is closed, does that mean the docs have been updated to explain the need to call jest.spyOn(global, 'setTimeout')? Without that, I think you’re going to continue to get confused users and more duplicates of this bug. They docs for 27.0 effectively still document legacy mode.

[github-actions]

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