code: def df():
      "Base DataFrame fixture"
      return pd.DataFrame(
          {"a": [1, np.nan, 3], "b": [2, 3, 1], "c": [2, np.nan, 9]}
      )
  
file_path: pyjanitor/tests/functions/test_coalesce.py
imports: import numpy
  import pandas
  import pytest
  from pandas.testing import assert_frame_equal
label_desc: Use image node_id 1 for calling a global function with example usage: df() and returns: pd