code: def test_synch_bn_pytorch_large_world(self) -> None:
      world_size = 4
      group_size = 2
      with with_temp_files(count=1) as sync_file:
          mp.spawn(
              self._test_synch_bn_pytorch_worker,
              (world_size, group_size, sync_file),
              nprocs=world_size,
          )
  
file_path: vissl/tests/test_model_helpers.py
imports: import unittest
  import torch
  import torch.multiprocessing
  import torch.nn
  from parameterized import param, parameterized
  from torch.nn.parallel import DistributedDataParallel
  from vissl.config import AttrDict
  from vissl.models.model_helpers import convert_sync_bn, split_world_in_process_groups
  from vissl.utils.env import set_env_vars
  from vissl.utils.test_utils import gpu_test, init_distributed_on_file, with_temp_files
label_desc: Use image node_id 3 for calling the TestModelHelpers obj's underlying member method code with example usage: obj.test_synch_bn_pytorch_large_world() without return types