code: def test_first_subset(self, frame_or_series):
      ts = DataFrame(
          np.random.default_rng(2).standard_normal((100, 4)),
          columns=Index(list("ABCD"), dtype=object),
          index=date_range("2000-01-01", periods=100, freq="12h"),
      )
      ts = tm.get_obj(ts, frame_or_series)
      with tm.assert_produces_warning(
          FutureWarning, match=deprecated_msg
      ):
          result = ts.first("10d")
          assert len(result) == 20
  
      ts = DataFrame(
          np.random.default_rng(2).standard_normal((100, 4)),
          columns=Index(list("ABCD"), dtype=object),
          index=date_range("2000-01-01", periods=100, freq="D"),
      )
      ts = tm.get_obj(ts, frame_or_series)
      with tm.assert_produces_warning(
          FutureWarning, match=deprecated_msg
      ):
          result = ts.first("10d")
          assert len(result) == 10
  
      with tm.assert_produces_warning(
          FutureWarning, match=deprecated_msg
      ):
          result = ts.first("3ME")
          expected = ts[:"3/31/2000"]
          tm.assert_equal(result, expected)
  
      with tm.assert_produces_warning(
          FutureWarning, match=deprecated_msg
      ):
          result = ts.first("21D")
          expected = ts[:21]
          tm.assert_equal(result, expected)
  
      with tm.assert_produces_warning(
          FutureWarning, match=deprecated_msg
      ):
          result = ts[:0].first("3ME")
          tm.assert_equal(result, ts[:0])
  
file_path: pandas/pandas/tests/frame/methods/test_first_and_last.py
imports: import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, bdate_range, date_range
  import pandas._testing
label_desc: Use image node_id 1 for calling the TestFirst obj's underlying member method code with example usage: obj.test_first_subset(frame_or_series) without return types