Move test helpers

[flying-sheep]

Things in tests shouldn’t be imported.

An alternative would be to move all that code into conftest and define that parameter set as fixture:

@pytest.fixture(scope="session", params=ARRAY_TYPES_MEM)
def array_type_mem(request: pytest.FixtureRequest) -> Callable[[ArrayLike], csr_matrix | csc_matrix | np.ndarray]:
    return request.param

then you can just do

@pytest.mark.parametrize("metric", ["sum", "mean", "var", "count_nonzero"])
def test_aggregate_vs_pandas(metric, array_type_mem):
    ...