code: def test_unsorted_dates_slice(df_dates):
      """Raise Error if the date column is unsorted."""
      df_dates = df_dates.iloc[:, ::-1]
      with pytest.raises(
          ValueError,
          match="The DatetimeIndex should be monotonic increasing.",
      ):
          df_dates.select_columns(slice("2011-01-31", "2011-03-31"))
  
imports: import datetime
  import re
  from itertools import product
  import numpy
  import pandas
  import pytest
  from pandas.api.types import is_numeric_dtype
  from pandas.testing import assert_frame_equal
  from janitor.functions.utils import DropLabel, get_columns, patterns
label_desc: Use image node_id 22 for calling a global function with example usage: test_unsorted_dates_slice(df_dates) without return types