def METHOD_NAME(self):
    tmp_dir = tempfile.TemporaryDirectory()
    dict_file = osp.join(tmp_dir.name, 'fake_chars.txt')
    create_dummy_dict_file(dict_file)
    # test diction cfg
    dict_cfg = dict(
        type='Dictionary',
        dict_file=dict_file,
        with_start=True,
        with_end=True,
        same_start_end=False,
        with_padding=True,
        with_unknown=True)
    decoder = BaseDecoder(dictionary=dict_cfg)
    with self.assertRaises(NotImplementedError):
        decoder.forward_train(None, None, None)
    tmp_dir.cleanup()