code: def test_fake_pg_device_mesh(self):
      fake_store = FakeStore()
      init_process_group(
          "fake", store=fake_store, rank=0, world_size=self.world_size
      )
      device_type = "cuda" if torch.cuda.is_available() else "cpu"
      mesh = DeviceMesh(device_type, torch.arange(self.world_size))
  
      local_tensor = torch.randn(2, 8)
      global_tensor = funcol.all_gather_tensor(
          local_tensor, gather_dim=0, group=(mesh, 0)
      )
      self.assertEqual(global_tensor.shape, (self.world_size * 2, 8))
  
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 8 for calling the DeviceMeshTest obj's underlying member method code with example usage: obj.test_fake_pg_device_mesh() without return types