code: def test_trainer_not_set(self):
      with self.assertRaises(Trainer.TrainerInitializationException):
          self.trainer.train()
  
imports: from tests.base_case import ChatBotTestCase
  from chatterbot.trainers import Trainer
  from chatterbot.conversation import Statement
label_desc: Use image node_id 2 for calling the TrainingTests obj's underlying member method code with example usage: obj.test_trainer_not_set() without return types