code: def testClose(self):
      saver = mock.create_autospec(
          policy_saver.PolicySaver, instance=True
      )
      async_saver = async_policy_saver.AsyncPolicySaver(saver)
      path = os.path.join(self.get_temp_dir(), "save_model")
  
      self.evaluate(tf.compat.v1.global_variables_initializer())
      async_saver.save(path)
      self.assertTrue(async_saver._save_thread.is_alive())
  
      async_saver.close()
      saver.save.assert_called_once()
  
      self.assertFalse(async_saver._save_thread.is_alive())
  
      with self.assertRaises(ValueError):
          async_saver.save(path)
  
file_path: agents/tf_agents/policies/async_policy_saver_test.py
imports: import os
  from absl.testing.absltest import mock
  import tensorflow
  from tf_agents.networks import q_network
  from tf_agents.policies import async_policy_saver
  from tf_agents.policies import policy_saver
  from tf_agents.policies import q_policy
  from tf_agents.specs import tensor_spec
  from tf_agents.trajectories import time_step
  from tf_agents.utils import common
  from tf_agents.utils import test_utils
label_desc: Use image node_id 5 for calling the AsyncPolicySaverTest obj's underlying member method code with example usage: obj.testClose() without return types