code: def test_stage_histogram(self, dataframe_json, msg):
      df = pd.read_json(dataframe_json)
      chart = runtime_by_region_vis.stage_histogram(
          df, title="chart title"
      )
      self.assertTrue(is_an_altair_chart(chart), msg=msg)
      chart_json = chart.to_json()
      self.assertIn("chart title", chart_json)
  
imports: import io
  from absl.testing import absltest
  from absl.testing import parameterized
  import pandas
  from deepvariant import runtime_by_region_vis
  from deepvariant import testdata
label_desc: Use image node_id 7 for calling the RuntimeByRegionVisTest obj's underlying member method code with example usage: obj.test_stage_histogram(dataframe_json, msg) without return types