code: def test__df_index_name_with_named_multi_index(self) -> None:
      data = io.StringIO(
          """\
  Fruit,Color,Count,Price
  Apple,Red,3,$1.29
  Apple,Green,9,$0.99
  Pear,Red,25,$2.59
  Pear,Green,26,$2.79
  Lime,Green,99,$0.39
  """
      )
      df = pd.read_csv(data).set_index(["Fruit", "Color"])
      assert df.index.names == ["Fruit", "Color"]
      assert bms.ColumnDataSource._df_index_name(df) == "Fruit_Color"
  
imports: from __future__ import annotations
  import pytest
  import datetime
  import io
  import numpy
  import pandas
  from bokeh.models import Selection
  from bokeh.util.serialization import convert_datetime_array
  from bokeh.util.warnings import BokehDeprecationWarning
  import bokeh.models.sources
label_desc: Use image node_id 29 for calling the TestColumnDataSource obj's underlying member method code with example usage: obj.test__df_index_name_with_named_multi_index() without return types