code: def test_basic(self) -> None:
      val = bt.stack("foo", "baz")
      assert isinstance(val, Expr)
      assert isinstance(val.expr, Stack)
      assert val.expr.fields == ("foo", "baz")
  
imports: from __future__ import annotations
  import pytest
  from bokeh.core.property.vectorization import Expr, Field
  from bokeh.models import CategoricalColorMapper, CategoricalMarkerMapper, CategoricalPatternMapper, CumSum, Dodge, EqHistColorMapper, FactorRange, Jitter, LinearColorMapper, LogColorMapper, Stack
  from tests.support.util.api import verify_all
  import bokeh.transform
label_desc: Use image node_id 1 for calling the Test_stack obj's underlying member method code with example usage: obj.test_basic() without return types