code: def test_str_bracket_labels():
      text = "((S (VP (VB Unban)) (NP (NNP Mox) (NNP Opal))))"
      expected = "(_ROOT (_S (_VP (_VB Unban )_VB )_VP (_NP (_NNP Mox )_NNP (_NNP Opal )_NNP )_NP )_S )_ROOT"
  
      trees = tree_reader.read_trees(text)
      assert len(trees) == 1
      assert "{:L}".format(trees[0]) == expected
  
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 18 for calling a global function with example usage: test_str_bracket_labels() without return types