code: def test_unique_labels():
      """
      Test getting the unique labels from a tree
  
      Assumes tree_reader works, which should be fine since it is tested elsewhere
      """
      text = "((SBARQ (WHNP (WP Who)) (SQ (VP (VBZ sits) (PP (IN in) (NP (DT this) (NN seat))))) (. ?))) ((SBARQ (WHNP (WP Who)) (SQ (VP (VBZ sits) (PP (IN in) (NP (DT this) (NN seat))))) (. ?)))"
  
      trees = tree_reader.read_trees(text)
  
      labels = Tree.get_unique_constituent_labels(trees)
      expected = ["NP", "PP", "ROOT", "SBARQ", "SQ", "VP", "WHNP"]
      assert labels == 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 4 for calling a global function with example usage: test_unique_labels() without return types