code: def test_mgrid_size_none_handling(self, start, stop, step, expected):
      # regression test None value handling for
      # start and step values used by mgrid;
      # internally, this aims to cover previously
      # unexplored code paths in nd_grid()
      grid = mgrid[start:stop:step, start:stop:step]
      # need a smaller grid to explore one of the
      # untested code paths
      grid_small = mgrid[start:stop:step]
      assert_equal(grid.size, expected[0])
      assert_equal(grid_small.size, expected[1])
  
imports: import functools
  from unittest import expectedFailure, skipIf
  from pytest import raises
  from torch.testing._internal.common_utils import instantiate_parametrized_tests, parametrize, run_tests, TEST_WITH_TORCHDYNAMO, TestCase, xpassIfTorchDynamo
label_desc: Use image node_id 5 for calling the TestGrid obj's underlying member method code with example usage: obj.test_mgrid_size_none_handling(start, stop, step, expected) without return types