code: def test_learn_response(self):
      previous_response = Statement(text="Define Hemoglobin.")
      statement = Statement(
          text="Hemoglobin is an oxygen-transport metalloprotein."
      )
      self.chatbot.learn_response(statement, previous_response)
      results = list(self.chatbot.storage.filter(text=statement.text))
  
      self.assertEqual(len(results), 1)
  
imports: from tests_django.base_case import ChatterBotTestCase
  from chatterbot.conversation import Statement
label_desc: Use image node_id 21 for calling the ChatBotTests obj's underlying member method code with example usage: obj.test_learn_response() without return types