def METHOD_NAME(self):
    from parlai.agents.hugging_face.dict import Gpt2DictionaryAgent
    from parlai.core.params import ParlaiParser
    parser = ParlaiParser(False, False)
    parser.set_defaults(gpt2_size="small", add_special_tokens=True, fp16=True)
    Gpt2DictionaryAgent.add_cmdline_args(parser, partial_opt=None)
    with testing_utils.tempdir() as tmpdir:
        opt = parser.parse_kwargs(dict_file=os.path.join(tmpdir, 'dict'))
        dict_agent = Gpt2DictionaryAgent(opt)
        oldtokens = dict_agent.txt2vec("Hi VOLDEMORT")
        prevlen = len(dict_agent)
        dict_agent.add_additional_special_tokens(["VOLDEMORT"])
        newlen = len(dict_agent)
        assert newlen == prevlen + 1
        tokens = dict_agent.txt2vec("Hi VOLDEMORT")
        assert tokens != oldtokens
        assert len(tokens) < len(oldtokens)