code: def null_df():
      np.random.seed([3, 1415])
      df = pd.DataFrame(np.random.choice((1, np.nan), (10, 2)))
      df["2"] = np.nan * 10
      df["3"] = np.nan * 10
      return df
  
file_path: pyjanitor/tests/conftest.py
imports: import os
  import numpy
  import pandas
  import pytest
  from janitor.testing_utils import date_data
label_desc: Use image node_id 4 for calling a global function with example usage: null_df() and returns: df