code: def test_nospecialtok(self):
      with self.assertRaises(RuntimeError):
          create_agent(
              {
                  "model": "hugging_face/gpt2",
                  "add_special_tokens": False,
                  "batchsize": 2,
              }
          )
  
      opt = {
          "model": "hugging_face/gpt2",
          "gpt2_size": "small",
          "text_truncate": 16,
          "label_truncate": 8,
          "beam_min_length": 8,
          "inference": "beam",
          "beam_size": 1,
          "batchsize": 1,
          "add_special_tokens": False,
          "fp16": True,
      }
      gpt2 = create_agent(opt)
      gpt2.observe({"text": "My name is", "episode_done": True})
      response = gpt2.act()
      assert response["text"] == " John. I'm a man of"
  
imports: import unittest
  from parlai.core.agents import create_agent
  import parlai.utils.testing
  import parlai.scripts.multiprocessing_train
  import parlai.scripts.build_dict
  import os
  import copy
label_desc: Use image node_id 4 for calling the TestGpt2 obj's underlying member method code with example usage: obj.test_nospecialtok() without return types