code: def test_len_column_names_less_than_2(df):
      """Raise Error if column_names length is less than 2."""
      with pytest.raises(ValueError):
          df.coalesce("a")
  
file_path: pyjanitor/tests/functions/test_coalesce.py
imports: import numpy
  import pandas
  import pytest
  from pandas.testing import assert_frame_equal
label_desc: Use image node_id 5 for calling a global function with example usage: test_len_column_names_less_than_2(df) without return types