code: def test_init(self):
      self.assertEqual(self.vocab.size, 3)
      self.assertListEqual(self.vocab.idx2tok, ["a", "b", "c"])
  
      tok2idx = defaultdict()
      for tok in self.tokens:
          tok2idx.setdefault(tok, len(tok2idx))
      self.assertDictEqual(self.vocab.tok2idx, tok2idx)
  
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 2 for calling the TestVocabulary obj's underlying member method code with example usage: obj.test_init() without return types