code: def test_remove_duplicates(df):
      output = remove_duplicates(
          df, cols=["cord_uid", "doi", "title", "license", "url"]
      )
      assert True not in output.duplicated(["cord_uid"]).values
  
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 2 for calling a global function with example usage: test_remove_duplicates(df) without return types