code: def as_string(self):
      return "\n".join(self.lines)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import functools
  import os
  import tempfile
  from unittest import mock
  from absl import logging
  from absl.testing import parameterized
  import tensorflow
  import tensorflow_probability
  from tf_agents.bandits.agents import exp3_agent
  from tf_agents.bandits.agents.examples.v2 import trainer
  from tf_agents.bandits.agents.examples.v2 import trainer_test_utils
  from tf_agents.bandits.environments import environment_utilities
  from tf_agents.bandits.environments import random_bandit_environment
  from tf_agents.bandits.environments import stationary_stochastic_py_environment
  from tf_agents.bandits.environments import wheel_py_environment
  from tf_agents.bandits.metrics import tf_metrics
  from tf_agents.environments import tf_py_environment
  from tf_agents.metrics import export_utils
  from tf_agents.specs import tensor_spec
label_desc: Use image node_id 3 for calling the MockLog obj's underlying member method code with example usage: obj.as_string() and returns: str