code: def test_column_names_iterable_type(null_df, column_names):
      result = null_df.fill_empty(column_names=column_names, value=3)
      excepted = null_df.fillna(3)
  
      assert result.equals(excepted)
  
imports: import pandas
  import pytest
label_desc: Use image node_id 3 for calling a global function with example usage: test_column_names_iterable_type(null_df, column_names) without return types