code: def test_call(self):
      target = mock.MagicMock()
      w = snapshot_writers.SimpleWriter()
      w.save = mock.MagicMock()
      with utils.tempdir() as tempd:
          w("myfile.dat", tempd, target)
  
      assert w.save.call_count == 1
  
imports: import multiprocessing
  import threading
  import unittest
  import mock
  from chainer import testing
  from chainer.training.extensions import snapshot_writers
  from chainer import utils
label_desc: Use image node_id 1 for calling the TestSimpleWriter obj's underlying member method code with example usage: obj.test_call() without return types