code: def test_basic(self, date_range_frame):
      # Explicitly cast to float to avoid implicit cast when setting np.nan
      df = date_range_frame.astype({"A": "float"})
      N = 50
      df.loc[df.index[15:30], "A"] = np.nan
      dates = date_range("1/1/1990", periods=N * 3, freq="25s")
  
      result = df.asof(dates)
      assert result.notna().all(1).all()
      lb = df.index[14]
      ub = df.index[30]
  
      dates = list(dates)
  
      result = df.asof(dates)
      assert result.notna().all(1).all()
  
      mask = (result.index >= lb) & (result.index < ub)
      rs = result[mask]
      assert (rs == 14).all(1).all()
  
file_path: pandas/pandas/tests/frame/methods/test_asof.py
imports: import numpy
  import pytest
  from pandas._libs.tslibs import IncompatibleFrequency
  from pandas import DataFrame, Period, Series, Timestamp, date_range, period_range, to_datetime
  import pandas._testing
label_desc: Use image node_id 1 for calling the TestFrameAsof obj's underlying member method code with example usage: obj.test_basic(date_range_frame) without return types