code: def test_no_sync_before_first_forward(self):
      group = DummyProcessGroup(rank=0, size=1)
      dummy_group_reduce_scatter = DummyProcessGroup(
          rank=group.rank(), size=group.size()
      )
      config = {
          "process_group_reduce_scatter",
          dummy_group_reduce_scatter,
      }
      model = self.get_wrapped_model(group, config, add_bn=False)
      batch = model.module.get_input(torch.device("cuda"))
      with model.no_sync():
          output = model(*batch)
          loss = model.module.get_loss(batch, output)
          loss.backward()
      output = model(*batch)
      loss = model.module.get_loss(batch, output)
      loss.backward()
  
imports: import contextlib
  import functools
  import itertools
  import unittest
  from unittest.mock import patch
  from parameterized import parameterized
  import torch
  from fairscale.fair_dev.testing.testing import DummyProcessGroup, make_cudnn_deterministic, objects_are_equal
  from fairscale.nn.data_parallel import FullyShardedDataParallel
  from .test_fsdp import DistributedTest, NestedWrappedModule, rename_test, spawn_and_init
label_desc: Use image node_id 5 for calling the TestGradAcc obj's underlying member method code with example usage: obj.test_no_sync_before_first_forward() without return types