code: def test_get_text_index_string_four_characters(self):
      bigram_string = self.tagger.get_text_index_string("ABCD")
  
      self.assertEqual(bigram_string, "abcd")
  
imports: from unittest import TestCase
  from chatterbot import languages
  from chatterbot import tagging
label_desc: Use image node_id 14 for calling the PosLemmaTaggerTests obj's underlying member method code with example usage: obj.test_get_text_index_string_four_characters() without return types