code: def test_series_multiindex_dataframe(df):
      """
      Test expand_grid output
      if the DataFrame's columns is a MultiIndex.
      """
      A = df["a"]
      B = df.iloc[:, [1, 2]]
      B.columns = pd.MultiIndex.from_arrays([["C", "D"], B.columns])
      others = {"A": A, "B": B}
      result = expand_grid(others=others)
      A = df.loc[:, ["a"]]
      expected = A.assign(key=1).merge(
          B.droplevel(level=1, axis=1), how="cross"
      )
      expected = expected.drop(columns="key")
      expected.columns = pd.MultiIndex.from_tuples(
          [
              ("A", "a", ""),
              ("B", "C", "Bell__Chart"),
              ("B", "D", "decorated-elephant"),
          ],
      )
      assert_frame_equal(result, expected)
  
imports: from functools import reduce
  import numpy
  import pandas
  import pytest
  from hypothesis import given, settings
  from pandas.testing import assert_frame_equal
  import janitor
  from janitor.functions.expand_grid import expand_grid
  from janitor.testing_utils.strategies import categoricaldf_strategy, df_strategy
label_desc: Use image node_id 13 for calling a global function with example usage: test_series_multiindex_dataframe(df) without return types