code: def test_short_run_ext(self):
      # Nothing passed, return self
      self.assertEqual(
          self.data.ta.short_run(append=True).shape, self.data.shape
      )
  
      fast = self.data.ta.ema(8)
      slow = self.data.ta.ema(21)
      self.data.ta.short_run(fast, slow, append=True)
      self.assertIsInstance(self.data, DataFrame)
      self.assertEqual(self.data.columns[-1], "SR_2")
  
imports: from .config import sample_data
  from .context import pandas_ta
  from unittest import skip, TestCase
  from pandas import DataFrame
label_desc: Use image node_id 18 for calling the TestTrendExtension obj's underlying member method code with example usage: obj.test_short_run_ext() without return types