code: def test_allreduce_persistent_cpu(self):
      comm = chainermn.create_communicator("naive")
      model = ExampleModel()
      self._test(comm, model, False, False)  # CPU test (numpy)
      self._test(comm, model, False, True)
  
file_path: chainer/tests/chainermn_tests/extensions_tests/test_allreduce_persistent.py
imports: import chainer
  import chainer.testing
  import chainer.testing.attr
  import unittest
  import chainermn
  from chainermn.testing.device import get_device
label_desc: Use image node_id 2 for calling the TestAllreducePersistent obj's underlying member method code with example usage: obj.test_allreduce_persistent_cpu() without return types