code: def test_save(self):
      self.vocab.save("tests/vocab.pkl")
      loaded_vocab = Vocabulary.load("tests/vocab.pkl")
      self.assertListEqual(self.vocab.idx2tok, loaded_vocab.idx2tok)
  
imports: import unittest
  from collections import defaultdict
  import numpy
  import numpy.testing
  from cornac.data import TextModality, ReviewModality
  from cornac.data.text import SPECIAL_TOKENS, DEFAULT_PRE_RULES, BaseTokenizer, Vocabulary, CountVectorizer, TfidfVectorizer
label_desc: Use image node_id 5 for calling the TestVocabulary obj's underlying member method code with example usage: obj.test_save() without return types