code: def test_async_mode_stop_on_dead(self):
      stream = StringIO()
      with contextlib.redirect_stdout(stream):
          with self.call_init(mode="async", flush_period=0.5) as exp:
              update_freq = 1
              default_freq = (
                  exp._op_processor.STOP_QUEUE_STATUS_UPDATE_FREQ_SECONDS
              )
              try:
                  exp._op_processor.STOP_QUEUE_STATUS_UPDATE_FREQ_SECONDS = (
                      update_freq
                  )
                  exp._op_processor._backend.execute_operations = Mock(
                      side_effect=ValueError
                  )
                  exp["some/variable"] = 13
                  exp.stop()
              finally:
                  exp._op_processor.STOP_QUEUE_STATUS_UPDATE_FREQ_SECONDS = (
                      default_freq
                  )
  
      self.assertIn(
          "NeptuneSynchronizationAlreadyStopped", stream.getvalue()
      )
  
imports: import contextlib
  import os
  import time
  import unittest
  from abc import abstractmethod
  from io import StringIO
  from unittest.mock import Mock
  from neptune.exceptions import MetadataInconsistency, MissingFieldException, NeptuneOfflineModeFetchException, NeptuneSynchronizationAlreadyStoppedException, TypeDoesNotSupportAttributeException
label_desc: Use image node_id 9 for calling the AbstractExperimentTestMixin obj's underlying member method code with example usage: obj.test_async_mode_stop_on_dead() without return types