Four tests fail on single-CPU machines

[sanvila]

Hello. On AWS machines of type m7a.medium and r7a.medium, which incidentally have a single CPU, the Debian package for version 0.11.1 always fail to build:

=================================== FAILURES ===================================
____________________________ test_debounced_leading ____________________________

    def test_debounced_leading() -> None:
        mock1 = Mock()
        f1 = debounced(mock1, timeout=10, leading=True)
        f2 = Mock()
    
        for _ in range(10):
            f1()
            f2()
    
        time.sleep(0.1)
>       assert mock1.call_count == 2
E       AssertionError: assert 1 == 2
E        +  where 1 = <Mock id='139801139221504'>.call_count

tests/test_throttler.py:36: AssertionError
________________________________ test_throttled ________________________________

    def test_throttled() -> None:
        mock1 = Mock()
        f1 = throttled(mock1, timeout=10, leading=True)
        f2 = Mock()
    
        for _ in range(10):
            f1()
            f2()
    
        time.sleep(0.1)
>       assert mock1.call_count == 2
E       AssertionError: assert 0 == 2
E        +  where 0 = <Mock id='139801140996688'>.call_count

tests/test_throttler.py:50: AssertionError
___________________________ test_throttled_trailing ____________________________

    def test_throttled_trailing() -> None:
        mock1 = Mock()
        f1 = throttled(mock1, timeout=10, leading=False)
        f2 = Mock()
    
        for _ in range(10):
            f1()
            f2()
    
        time.sleep(0.1)
>       assert mock1.call_count == 1
E       AssertionError: assert 0 == 1
E        +  where 0 = <Mock id='139801141000048'>.call_count

tests/test_throttler.py:64: AssertionError
________________ test_throttled_debounced_signature[throttled] _________________

deco = <function throttled at 0x7f25fef3ce00>

    @pytest.mark.parametrize("deco", [debounced, throttled])
    def test_throttled_debounced_signature(deco: Callable) -> None:
        mock = Mock()
    
        @deco(timeout=0, leading=True)
        def f1(x: int) -> None:
            """Doc."""
            mock(x)
    
        # make sure we can still inspect the signature
        assert signature(f1).parameters["x"] == Parameter(
            "x", Parameter.POSITIONAL_OR_KEYWORD, annotation=int
        )
    
        # make sure these are connectable
        sig = SignalInstance((int, int, int))
        sig.connect(f1)
        sig.emit(1, 2, 3)
>       mock.assert_called_once_with(1)

tests/test_throttler.py:106: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <Mock id='139801139219152'>, args = (1,), kwargs = {}
msg = "Expected 'mock' to be called once. Called 0 times."

    def assert_called_once_with(self, /, *args, **kwargs):
        """assert that the mock was called exactly once and that that call was
        with the specified arguments."""
        if not self.call_count == 1:
            msg = ("Expected '%s' to be called once. Called %s times.%s"
                   % (self._mock_name or 'mock',
                      self.call_count,
                      self._calls_repr()))
>           raise AssertionError(msg)
E           AssertionError: Expected 'mock' to be called once. Called 0 times.

/usr/lib/python3.13/unittest/mock.py:990: AssertionError
=========================== short test summary info ============================
FAILED tests/test_throttler.py::test_debounced_leading - AssertionError: asse...
FAILED tests/test_throttler.py::test_throttled - AssertionError: assert 0 == 2
FAILED tests/test_throttler.py::test_throttled_trailing - AssertionError: ass...
FAILED tests/test_throttler.py::test_throttled_debounced_signature[throttled]
================== 4 failed, 570 passed, 21 skipped in 1.62s ===================

Is this a bug in the tests, or it is a bug in the code? Should I use os.cpu_count() == 1 inside a skipif to skip them?

Thanks.

Edit: At least once this test also failed for me on a machine with 2 vCPUs:

FAILED tests/test_throttler.py::test_throttled_trailing - AssertionError: ass...

[Czaki]

May you check what happened it you increase sleep to 0.2? I expect that it could be a problem with the process scheduler.

[sanvila]

Using 0.2 does not fix the problem It still fails.

I forgot: To reproduce please try booting with GRUB_CMDLINE_LINUX="nr_cpus=1". If that does not help to reproduce the problem, I can offer a VM to test (I'm reachable at debian.org).

Thanks.

[Czaki]

hm. I need to think. We meet this class of problem on github CI. But most often restart of CI helps.

I think that the problem is on some server machines, the thread switch is not called enough frequently. I still do not found way to properly workaround it..

[tlambert03]

Hey guys, any updates here? Is there anything we can likely do here?