Unreliable imap test in test_multiprocessing with fixed sleep duration

[nascheme]

Bug report

I'm getting a failure in CI (on Windows) that produces the log output below. I believe it's due to the test case being unreliable since it uses fixed sleep durations, i.e. time.sleep(0.2). The test would be more reliable if it used bounded waits.

FAIL: test_imap_and_imap_unordered_with_buffersize_when_buffer_is_full (test.test_multiprocessing_spawn.test_threads.WithThreadsTestPool.test_imap_and_imap_unordered_with_buffersize_when_buffer_is_full) (method_name='imap')
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\support\__init__.py", line 1121, in wrapper
    func(self, *args, **kwargs, **subtest_kwargs)
    ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\a\cpython\cpython\Lib\test\_test_multiprocessing.py", line 3227, in test_imap_and_imap_unordered_with_buffersize_when_buffer_is_full
    self.assertEqual(last_produced_task_arg.value, processes + 2)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 5 != 6

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-158975: Replace fixed sleeps in multiprocessing tests #158977