code: def test_vocab_size_lower_on(self):
      word_vocab_size = 4
      char_vocab_size = 4
      label_size = 3
  
      # lower is effective.
      it = IndexTransformer(lower=True)
      it.fit(self.x, self.y)
      self.assertEqual(
          it.word_vocab_size, word_vocab_size + 2
      )  # pad, unk
      self.assertEqual(
          it.char_vocab_size, char_vocab_size + 2
      )  # pad, unk
      self.assertEqual(it.label_size, label_size + 1)
  
imports: import os
  import shutil
  import unittest
  import numpy
  from anago.preprocessing import IndexTransformer, pad_nested_sequences
label_desc: Use image node_id 4 for calling the TestIndexTransformer obj's underlying member method code with example usage: obj.test_vocab_size_lower_on() without return types