Fix MPI test teardown failure caused by unpicklable pytest tmpdir fixture

[Copilot]

test_loggingMPI was failing with AttributeError: Can't pickle local object '_BaseExitStack._create_cb_wrapper.<locals>._exit_wrapper' in all MPI ranks.

Root cause

Using pytest's tmpdir fixture triggers TempPathFactory.getbasetemp(), which registers callbacks on an internal ExitStack. In pytest ≥8.1, these callbacks are wrapped in _create_cb_wrapper.<locals>._exit_wrapper — a local function that cannot be pickled. pytest-isolate-mpi attempts to pickle all session-scoped fixtures (including tmp_path_factory) during teardown via _cache_fixture_result, causing the teardown to error.

Fix

Replace the tmpdir fixture dependency in test_loggingMPI with tempfile.mkdtemp(), avoiding tmp_path_factory entirely. Rank 0 creates the directory, broadcasts the path string to all ranks, and cleans up after the test.

@pytest.mark.mpi4py
@pytest.mark.mpi(ranks=[1, 4])
def test_loggingMPI(comm, mpi_ranks):
    # `mpi_ranks` is a pytest fixture required by pytest-isolate-mpi. Do not remove.
    import tempfile, shutil

    tmpdir = tempfile.mkdtemp() if comm.rank == 0 else None
    tmpdir = comm.bcast(tmpdir, root=0)
    try:
        test_logging(tmpdir, False, False)
    finally:
        if comm.rank == 0:
            shutil.rmtree(tmpdir, ignore_errors=True)

[github-actions]

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