code: def test_allreduce_persistent_gpu(self):
      comm = chainermn.create_communicator("flat")
      model = ExampleModel()
      self._test(comm, model, True, False)  # GPU test (CuPy)
      self._test(comm, model, True, 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 3 for calling the TestAllreducePersistent obj's underlying member method code with example usage: obj.test_allreduce_persistent_gpu() without return types