________ test_nested_parallel_warnings[threading-multiprocessing-True] _________

parent_backend = 'threading', child_backend = 'multiprocessing', expected = True

    @with_multiprocessing
    @parametrize('parent_backend,child_backend,expected', [
        ('loky', 'multiprocessing', True), ('loky', 'loky', False),
        ('multiprocessing', 'multiprocessing', True),
        ('multiprocessing', 'loky', True),
        ('threading', 'multiprocessing', True),
        ('threading', 'loky', True),
    ])
    def test_nested_parallel_warnings(parent_backend, child_backend, expected):
    
        # no warnings if inner_n_jobs=1
>       Parallel(n_jobs=2, backend=parent_backend)(
            delayed(_assert_warning_nested)(
                backend=child_backend, inner_n_jobs=1,
                expected=False)
            for _ in range(5))

joblib/test/test_parallel.py:217: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
joblib/parallel.py:1056: in __call__
    self.retrieve()
joblib/parallel.py:935: in retrieve
    self._output.extend(job.get(timeout=self.timeout))
/nix/store/adnh88kc6cf2dc8fqfyvjmyyd86v52qn-python3-3.9.10/lib/python3.9/multiprocessing/pool.py:771: in get
    raise self._value
/nix/store/adnh88kc6cf2dc8fqfyvjmyyd86v52qn-python3-3.9.10/lib/python3.9/multiprocessing/pool.py:125: in worker
    result = (True, func(*args, **kwds))
joblib/_parallel_backends.py:595: in __call__
    return self.func(*args, **kwargs)
joblib/parallel.py:262: in __call__
    return [func(*args, **kwargs)
joblib/parallel.py:262: in <listcomp>
    return [func(*args, **kwargs)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

backend = 'multiprocessing', inner_n_jobs = 1, expected = False

    def _assert_warning_nested(backend, inner_n_jobs, expected):
        with warns(None) as records:
            parallel_func(backend=backend, inner_n_jobs=inner_n_jobs)
    
        if expected:
            # with threading, we might see more that one records
            if len(records) > 0:
                return 'backed parallel loops cannot' in records[0].message.args[0]
            return False
        else:
>           assert len(records) == 0
E           assert 2 == 0
E            +  where 2 = len(WarningsChecker(record=True))

joblib/test/test_parallel.py:202: AssertionError