code: def setup_communicator(gpu):
      if gpu:
          communicator = chainermn.create_communicator("flat")
          chainer.backends.cuda.get_device_from_id(
              communicator.intra_rank
          ).use()
      else:
          communicator = chainermn.create_communicator("naive")
  
      if communicator.size < 2:
          pytest.skip("This test is for multinode only")
  
      rank_next = communicator.rank + 1
      rank_prev = communicator.rank - 1
  
      if rank_prev < 0:
          rank_prev = None
  
      if rank_next >= communicator.size:
          rank_next = None
  
      return communicator, rank_prev, rank_next
  
imports: import chainer
  import chainer.backends
  from chainer.backends.cuda import cupy
  import chainer.functions
  import chainer.links
  import chainer.testing
  import chainer.testing.attr
  import chainermn
  import numpy
  import pytest
label_desc: Use image node_id 1 for calling a global function with example usage: setup_communicator(gpu) and returns: communicator,  rank_prev,  rank_next