code: def test_asof(self):
      N = 3
      rng = pd.date_range("1/1/1990", periods=N, freq="53s")
      df = tm.SubclassedDataFrame(
          {
              "A": [np.nan, np.nan, np.nan],
              "B": [np.nan, np.nan, np.nan],
              "C": [np.nan, np.nan, np.nan],
          },
          index=rng,
      )
  
      result = df.asof(rng[-2:])
      assert isinstance(result, tm.SubclassedDataFrame)
  
      result = df.asof(rng[-2])
      assert isinstance(result, tm.SubclassedSeries)
  
      result = df.asof("1989-12-31")
      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 26 for calling the TestDataFrameSubclassing obj's underlying member method code with example usage: obj.test_asof() without return types