code: def test_index(self):
      plugin = self.load_plugin(
          [
              self._RUN_WITH_SCALARS,
              self._RUN_WITH_LEGACY_HISTOGRAM,
              self._RUN_WITH_HISTOGRAM,
          ]
      )
      self.assertEqual(
          {
              # _RUN_WITH_SCALARS omitted: No histogram data.
              self._RUN_WITH_LEGACY_HISTOGRAM: {
                  self._LEGACY_HISTOGRAM_TAG: {
                      "displayName": self._LEGACY_HISTOGRAM_TAG,
                      "description": "",
                  },
              },
              self._RUN_WITH_HISTOGRAM: {
                  "%s/histogram_summary"
                  % self._HISTOGRAM_TAG: {
                      "displayName": self._DISPLAY_NAME,
                      "description": self._HTML_DESCRIPTION,
                  },
              },
          },
          plugin.index_impl(context.RequestContext(), experiment="exp"),
      )
  
imports: import collections.abc
  import os.path
  import tensorflow
  from tensorboard import errors
  from tensorboard import context
  from tensorboard.backend.event_processing import data_provider
  from tensorboard.backend.event_processing import plugin_event_multiplexer
  from tensorboard.backend.event_processing import tag_types
  from tensorboard.plugins import base_plugin
  from tensorboard.plugins.histogram import histograms_plugin
  from tensorboard.plugins.histogram import summary
  from tensorboard.util import test_util
label_desc: Use image node_id 6 for calling the HistogramsPluginTest obj's underlying member method code with example usage: obj.test_index() without return types