code: def test_get_text_index_string_single_character(self):
      bigram_string = self.tagger.get_text_index_string("🙂")
  
      self.assertEqual(bigram_string, "🙂")
  
imports: from unittest import TestCase
  from chatterbot import languages
  from chatterbot import tagging
label_desc: Use image node_id 10 for calling the PosLemmaTaggerTests obj's underlying member method code with example usage: obj.test_get_text_index_string_single_character() without return types