code: def _mock_list_tensors(
      self, ctx, *, experiment_id, plugin_name, run_tag_filter
  ):
      hparams_content = {
          "exp/session_1": {
              metadata.SESSION_START_INFO_TAG: self._serialized_plugin_data(
                  DATA_TYPE_SESSION_START_INFO,
                  self.session_1_start_info_,
              ),
          },
          "exp/session_2": {
              metadata.SESSION_START_INFO_TAG: self._serialized_plugin_data(
                  DATA_TYPE_SESSION_START_INFO,
                  self.session_2_start_info_,
              ),
          },
          "exp/session_3": {
              metadata.SESSION_START_INFO_TAG: self._serialized_plugin_data(
                  DATA_TYPE_SESSION_START_INFO,
                  self.session_3_start_info_,
              ),
          },
      }
      result = {}
      for run, tag_to_content in hparams_content.items():
          result.setdefault(run, {})
          for tag, content in tag_to_content.items():
              t = provider.TensorTimeSeries(
                  max_step=0,
                  max_wall_time=0,
                  plugin_content=content,
                  description="",
                  display_name="",
              )
              result[run][tag] = t
      return result
  
imports: import operator
  from unittest import mock
  import tensorflow
  from google.protobuf import text_format
  from tensorboard import context
  from tensorboard.data import provider
  from tensorboard.plugins import base_plugin
  from tensorboard.plugins.hparams import api_pb2
  from tensorboard.plugins.hparams import backend_context
  from tensorboard.plugins.hparams import metadata
  from tensorboard.plugins.hparams import plugin_data_pb2
label_desc: Use image node_id 2 for calling the BackendContextTest obj's underlying member method code with example usage: obj._mock_list_tensors(ctx) and returns: result