))      perturbation_mask_regions = perturbation.compute_perturbation_mask(ranks, 0)     assert np.all(perturbation_mask_regions == np.array([[0, 0], [0, 0]]))      perturbation_mask_regions = perturbation.compute_perturbation_mask(ranks, 0)     assert np.all(perturbation_mask_regions == np.array([[0, 0], [0, 0]]))      perturbation_mask_regions = perturbation.compute_perturbation_mask(ranks, 0)     assert np.all(perturbation_mask_regions == np.array([[0, 0], [0, 0]]))