docstr: This unit test verifies the ``noop`` hook registered case and a subsequent allreduce
  gives same result with no hook registered case.
docstr_tok: ["This","unit","test","verifies","the","``","noop","``","hook","registered","case","and","a","subsequent","allreduce","gives","same","result","with","no","hook","registered","case","."]
code: def test_ddp_comm_hook_noop_hook(self):
      """
      This unit test verifies the ``noop`` hook registered case and a subsequent allreduce
      gives same result with no hook registered case.
      """
      process_group = self._get_process_group_nccl()
  
      # No hook registered case, get the reference grads.
      reference_grads = self._get_grads(process_group, None)
      # Register hook case, get the hook grads.
      hook_grads = self._get_grads(process_group, DDPCommHookType.NOOP)
      # Apply a subsequent allreduce to average grads.
      hook_grads.div_(self.world_size)
      dist.all_reduce(hook_grads, group=process_group)
  
      torch.testing.assert_close(
          hook_grads, reference_grads, rtol=1e-5, atol=0
      )
  
imports: import os
  import sys
  import torch
  from torch import nn
  import torch.distributed
  from torch.distributed.algorithms.ddp_comm_hooks import DDPCommHookType, register_ddp_comm_hook
  from torch.nn.parallel import DistributedDataParallel
  from torch.testing._internal.common_distributed import MultiProcessTestCase, requires_nccl, skip_if_lt_x_gpu
  from torch.testing._internal.common_utils import run_tests, TEST_WITH_DEV_DBG_ASAN
label_desc: Use image node_id 12 for calling the DistributedDataParallelCommHookTest obj's underlying member method code with example usage: obj.test_ddp_comm_hook_noop_hook() without return types