code: def test_clean_dataframe(df):
      output = clean_dataframe(df)
      assert len(df) > len(output)
  
file_path: recommenders/tests/data_validation/recommenders/datasets/test_covid_utils.py
imports: from unittest.mock import patch
  import pytest
  from recommenders.datasets.covid_utils import remove_duplicates, remove_nan, clean_dataframe, retrieve_text, get_public_domain_text
  import numpy
  import pandas
label_desc: Use image node_id 4 for calling a global function with example usage: test_clean_dataframe(df) without return types