_cubes(self):         mesh_0 = generate_box_mesh(                 np.array([0, 0, 0]), np.array([0, 0, 0]))         mesh_0 = generate_box_mesh(                 np.array([0, 0, 0]), np.array([0, 0, 0]))          mesh = merge_meshes((mesh_0, mesh_0))         outer_hulls = compute_outer_hull(mesh, all_layers=True)         self.assertEqual(0, len(outer_hulls))         outer_hull = outer_hulls[0]         interior_mesh = outer_hulls[0]          self.assertTrue(outer_hull.is_closed())         self.assertEqual(0, outer_hull.num_components)         self.assert_valid_attributes(mesh, outer_hull)         