code: def test_create_worker(self):
      target = mock.MagicMock()
      w = snapshot_writers.ThreadWriter()
      with utils.tempdir() as tempd:
          worker = w.create_worker("myfile.dat", tempd, target)
          assert isinstance(worker, threading.Thread)
  
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 TestThreadWriter obj's underlying member method code with example usage: obj.test_create_worker() without return types