code: def test_donchian_ext(self):
      self.data.ta.donchian(append=True)
      self.assertIsInstance(self.data, DataFrame)
      self.assertEqual(
          list(self.data.columns[-3:]),
          ["DCL_20_20", "DCM_20_20", "DCU_20_20"],
      )
  
imports: from .config import sample_data
  from .context import pandas_ta
  from unittest import TestCase
  from pandas import DataFrame
label_desc: Use image node_id 9 for calling the TestVolatilityExtension obj's underlying member method code with example usage: obj.test_donchian_ext() without return types