code: def test_smoke_multinode_snapshot():
      t = mock.MagicMock()
      c = mock.MagicMock(side_effect=[True, False])
      w = mock.MagicMock()
      snapshot = extensions.snapshot(target=t, condition=c, writer=w)
      trainer = mock.MagicMock()
  
      comm = create_communicator("naive")
      replica_sets = []
      mn_snapshot = multi_node_snapshot(comm, snapshot, replica_sets)
  
      mn_snapshot.initialize(trainer)
      mn_snapshot(trainer)
      mn_snapshot(trainer)
      mn_snapshot.finalize()
  
      if comm.rank == 0:
          assert mn_snapshot.is_master
          assert c.call_count == 2
          assert w.call_count == 1
      else:
          assert not mn_snapshot.is_master
          assert c.call_count == 0
          assert w.call_count == 0
  
      comm.finalize()
  
imports: import mock
  import tempfile
  import pytest
  import chainer
  import chainer.links
  import chainer.functions
  from chainer.training import extensions
  from chainer.training import StandardUpdater
  from chainer.training import Trainer
  import chainermn
  from chainermn import create_communicator
  from chainermn.extensions import multi_node_snapshot
  from chainermn.extensions import _multi_node_snapshot
label_desc: Use image node_id 4 for calling a global function with example usage: test_smoke_multinode_snapshot() without return types