code: def test_basic(self, toy_df):
      groupby = GroupBy(["color", "group"])
      res = Stack()(toy_df, groupby, "x", {})
  
      assert_array_equal(res["x"], [0, 0, 1])
      assert_array_equal(res["y"], [1, 3, 3])
      assert_array_equal(res["baseline"], [0, 1, 0])
  
imports: from itertools import product
  import numpy
  import pandas
  from pandas.testing import assert_series_equal
  from numpy.testing import assert_array_equal, assert_array_almost_equal
  from seaborn._core.moves import Dodge, Jitter, Shift, Stack, Norm
  from seaborn._core.rules import categorical_order
  from seaborn._core.groupby import GroupBy
  import pytest
label_desc: Use image node_id 1 for calling the TestStack obj's underlying member method code with example usage: obj.test_basic(toy_df) without return types