code: def test_device_mesh_2d(self):
      mesh_tensor = torch.arange(4).reshape(2, 2)
      # construct a cuda device mesh
      mesh = DeviceMesh(self.device_type, mesh_tensor)
  
      # check all dim groups
      dim_to_subgroups = mesh.get_group()
  
      expected_ranks_by_dim = [[[0, 2], [1, 3]], [[0, 1], [2, 3]]]
      for dim, dim_group in enumerate(dim_to_subgroups):
          self.assertTrue(dim < 2)
          dim_ranks = expected_ranks_by_dim[dim]
  
          dim_group_size = get_world_size(dim_group)
          self.assertIsInstance(dim_group, ProcessGroup)
          self.assertEqual(dim_group_size, 2)
          global_ranks = [
              get_global_rank(dim_group, i)
              for i in range(dim_group_size)
          ]
          current_rank_expected_group_ranks = (
              dim_ranks[0]
              if self.rank in dim_ranks[0]
              else dim_ranks[1]
          )
          self.assertEqual(
              global_ranks, current_rank_expected_group_ranks
          )
  
imports: import os
  import torch
  import torch.distributed._functional_collectives
  from torch.distributed._tensor import DTensor
  from torch.distributed._tensor._collective_utils import mesh_all_to_all, mesh_broadcast, mesh_scatter
  from torch.distributed._tensor.placement_types import _Partial, Shard
  from torch.distributed.device_mesh import _mesh_resources, DeviceMesh, init_device_mesh
  from torch.distributed.distributed_c10d import get_global_rank, get_world_size, init_process_group, is_initialized, is_nccl_available, ProcessGroup
  from torch.testing._internal.common_utils import run_tests
  from torch.testing._internal.distributed._tensor.common_dtensor import DTensorTestBase, with_comms
  from torch.testing._internal.distributed.fake_pg import FakeStore
label_desc: Use image node_id 6 for calling the DeviceMeshTest obj's underlying member method code with example usage: obj.test_device_mesh_2d() without return types