code: def test_idx(self, idx_method):
      df = tm.SubclassedDataFrame(
          {"A": [1, 2, 3], "B": [4, 5, 6], "C": [7, 8, 9]}
      )
      result = getattr(df, idx_method)()
      assert isinstance(result, tm.SubclassedSeries)
  
imports: import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 22 for calling the TestDataFrameSubclassing obj's underlying member method code with example usage: obj.test_idx(idx_method) without return types