code: def test_skipna():
      """
      Overall test for skipna.
  
      TODO: Should be refactored into separate tests.
      """
      df = pd.DataFrame(
          {"x": ["a", "b", "c", np.nan], "y": [1, 2, 3, np.nan]}
      )
  
      def func(s):
          """Dummy helper func."""
          return s + "1"
  
      # Verify that applying function causes error
      with pytest.raises(Exception):
          df["x"].apply(func)
  
      result = df["x"].apply(skipna(func))
      assert (
          result.to_numpy()[:-1] == np.array(["a1", "b1", "c1"])
      ).all() and np.isnan(result.to_numpy()[-1])
  
imports: import numpy
  import pandas
  import pytest
  from janitor.utils import skipna
label_desc: Use image node_id 1 for calling a global function with example usage: test_skipna() and returns: unknown