code: def test_asof(self):
      N = 3
      rng = pd.date_range("1/1/1990", periods=N, freq="53s")
      s = tm.SubclassedSeries(
          {"A": [np.nan, np.nan, np.nan]}, index=rng
      )
  
      result = s.asof(rng[-2:])
      assert isinstance(result, tm.SubclassedSeries)
  
file_path: pandas/pandas/tests/series/test_subclass.py
imports: import numpy
  import pytest
  import pandas
  import pandas._testing
label_desc: Use image node_id 5 for calling the TestSeriesSubclassing obj's underlying member method code with example usage: obj.test_asof() without return types