code: def test_forked_cw(self, device_option):
      TestCase.test_counter += 1
      if os.getenv("COMM_RANK") is not None:
          self.run_test_distributed(
              self._test_allreduce_multicw, device_option=device_option
          )
      else:
          # Note: this test exercises the path where we fork a common world.
          # We therefore don't need a comm size larger than 2. It used to be
          # run with comm_size=8, which causes flaky results in a stress run.
          # The flakiness was caused by too many listening sockets being
          # created by Gloo context initialization (8 processes times
          # 7 sockets times 20-way concurrency, plus TIME_WAIT).
          with TemporaryDirectory() as tmpdir:
              self.run_test_locally(
                  self._test_allreduce_multicw,
                  comm_size=2,
                  device_option=device_option,
                  tmpdir=tmpdir,
              )
  
imports: from hypothesis import given, settings
  import hypothesis.strategies
  from multiprocessing import Process, Queue
  import numpy
  import os
  import pickle
  import tempfile
  import shutil
  from caffe2.python import core, workspace, dyndep
  import caffe2.python.hypothesis_test_util
  from gloo.python import IoError
label_desc: Use image node_id 14 for calling the TestCase obj's underlying member method code with example usage: obj.test_forked_cw(device_option) without return types