code: def test_str():
      stack = TreeStack(value=5, parent=None, length=1)
      stack = stack.push(3)
      stack = stack.push(1)
  
      assert str(stack) == "TreeStack(1, 3, 5)"
  
imports: import pytest
  from stanza.models.constituency.tree_stack import TreeStack
  from stanza.tests import *
label_desc: Use image node_id 3 for calling a global function with example usage: test_str() without return types