code: def test_offline_mode(self):
      with self.call_init(mode="offline") as exp:
          exp["some/variable"] = 13
          with self.assertRaises(NeptuneOfflineModeFetchException):
              exp["some/variable"].fetch()
  
          exp_dir = f"{exp.container_type.value}__{exp._id}"
          self.assertIn(exp_dir, os.listdir(".neptune/offline"))
          self.assertIn(
              "data-1.log", os.listdir(f".neptune/offline/{exp_dir}")
          )
  
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 4 for calling the AbstractExperimentTestMixin obj's underlying member method code with example usage: obj.test_offline_mode() without return types