code: def test_multi_node_bn_cpu(communicator_class, backend, dtype):
      comm = create_communicator(
          communicator_class, mpi_comm, use_gpu=False
      )
      check_multi_node_bn(comm, backend=backend, dtype=dtype)
      check_link_copyable(comm)
      comm.mpi_comm.barrier()
  
imports: import chainer
  from chainer.backends.cuda import cupy
  import chainer.testing
  import chainer.utils
  import mpi4py.MPI
  import numpy
  import pytest
  from chainermn.communicators.naive_communicator import NaiveCommunicator
  from chainermn.communicators.pure_nccl_communicator import PureNcclCommunicator
  from chainermn.links import MultiNodeBatchNormalization
  from chainermn import nccl
label_desc: Use image node_id 6 for calling a global function with example usage: test_multi_node_bn_cpu(communicator_class, backend, dtype) without return types