code: def test_non_method_functional(missingdata_df):
      """Checks the behaviour when `flag_nulls` is used as a function."""
      expected = missingdata_df.copy()
      expected["null_flag"] = [0, 1, 1] * 3
  
      df = flag_nulls(missingdata_df)
  
      assert_frame_equal(df, expected, check_dtype=False)
  
file_path: pyjanitor/tests/functions/test_flag_nulls.py
imports: import pandas
  import pytest
  from pandas.testing import assert_frame_equal
  from janitor.functions import flag_nulls
label_desc: Use image node_id 2 for calling a global function with example usage: test_non_method_functional(missingdata_df) without return types