code: def test_names_sep_pattern_both_none(df_checks):
      """Raise ValueError if neither names_sep nor names_pattern is provided."""
      msg = "Provide argument for either names_sep or names_pattern."
      with pytest.raises(ValueError, match=msg):
          df_checks.explode_index(
              axis="columns", names_sep=None, names_pattern=None
          )
  
file_path: pyjanitor/tests/functions/test_explode_index.py
imports: import pandas
  import pytest
  from pandas.testing import assert_frame_equal
label_desc: Use image node_id 6 for calling a global function with example usage: test_names_sep_pattern_both_none(df_checks) without return types