code: def test_load_demo_dataset():
      """
      Test load_demo_dataset function.
      """
      df = load_demo_dataset()
  
      assert isinstance(df, pd.Series)
      assert df.index.freq == "MS"
      assert df.index.is_monotonic_increasing
      assert df.index[0] == pd.Timestamp("1991-07-01")
      assert df.index[-1] == pd.Timestamp("2008-06-01")
      assert df.shape == (204,)
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_load_demo_dataset() without return types