code: def setup_cpu(self):
      self.comm = chainermn.create_communicator("naive")
      self.target = ExampleModel()
      self.target.a.W.data[:] = self.comm.rank
      self.target.b.W.data[:] = self.comm.rank + 1
      self.target.c.W.data[:] = self.comm.rank + 2
      self.target.a.W.grad[:] = 0
      self.target.b.W.grad[:] = 0
      self.target.c.W.grad[:] = 0
      self.actual_optimizer = chainer.GradientMethod()
      self.actual_optimizer.create_update_rule = mock.MagicMock
  
imports: import chainer
  import chainer.testing
  import chainer.testing.attr
  import chainermn
  import chainermn.testing
  import mock
  import numpy
  import pytest
label_desc: Use image node_id 1 for calling the TestMultiNodeOptimizer obj's underlying member method code with example usage: obj.setup_cpu() without return types