code: def test_compare_df_three_tables(tables):
      out = nbcollection.compare_df(
          tables=tables, ids=[1, 2, 3], scores_arg=None
      )
  
      assert out is None
  
imports: import pytest
  import pandas
  import numpy
  from sklearn_evaluation import NotebookCollection
  from sklearn_evaluation.nb import NotebookCollection
  from IPython.display import HTML
label_desc: Use image node_id 16 for calling a global function with example usage: test_compare_df_three_tables(tables) without return types