Enable tracemalloc for a single test/module

[Carreau]

I've tried to enable tracemalloc for a single set of tests, as there is a random ResourceWarning,
and runing globlally with TRACEMALLOC=20 is wayyyy to long.

Unfortunately setting a tracemalloc fixture with tracemalloc.start(20)/.stop(), meand that tracemalloc is disable beofre the warnings get printed;

So I still get the

Enable tracemalloc to get traceback where the object was allocated.
See https://docs.pytest.org/en/stable/how-to/capture-warnings.html#resource-warnings for more info

Do anyone has a tip on how I could have a proper tracemalloc and resource warnings for a single test ?

[Carreau]

I'm going to go with the following, it's ugly but seem to work.

@pytest.fixture()
def tracemalloc_resource_warning(recwarn, N=10):
    """fixture to enable tracemalloc for a single test, and report the
    location of the leaked resource

    We cannot only enable tracemalloc, as otherwise it is stopped just after the
    test, the frame cache is cleared by tracemalloc.stop() and thus the warning
    printing code get None when doing
    `tracemalloc.get_object_traceback(r.source)`.

    So we need to both filter the warnings to enable ResourceWarning, and loop
    through it print the stack before we stop tracemalloc and continue.

    """

    tracemalloc.start(N)
    with warnings.catch_warnings():
        warnings.simplefilter("always", category=ResourceWarning)
        yield None
    try:
        for r in recwarn:
            if r.category is ResourceWarning and r.source is not None:
                tb = tracemalloc.get_object_traceback(r.source)
                if tb:
                    info = f"Leaking resource:{r}\n |" + "\n |".join(tb.format())
                    # technically an Error and not a failure as we fail in the fixture
                    # and not the test
                    pytest.fail(info)
    finally:
        tracemalloc.stop()