code: def test_unique_words():
      """
      Test getting the unique words from a tree
      """
      text = "((SBARQ (WHNP (WP Who)) (SQ (VP (VBZ sits) (PP (IN in) (NP (DT this) (NN seat))))) (. ?)))"
  
      trees = tree_reader.read_trees(text)
  
      words = Tree.get_unique_words(trees)
      expected = ["?", "Who", "in", "seat", "sits", "this"]
      assert words == 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 6 for calling a global function with example usage: test_unique_words() without return types