code: def test_yield_preterminals():
      text = "((S (VP (VB Unban)) (NP (NNP Mox) (NNP Opal))))"
      trees = tree_reader.read_trees(text)
  
      preterminals = list(trees[0].yield_preterminals())
      assert len(preterminals) == 3
      assert str(preterminals) == "[(VB Unban), (NNP Mox), (NNP Opal)]"
  
imports: import pytest
  from stanza.models.constituency.parse_tree import Tree
  from stanza.models.constituency import tree_reader
  from stanza.tests import *
label_desc: Use image node_id 2 for calling a global function with example usage: test_yield_preterminals() without return types