code: def setup_class(cls):
      cls.special_tokens = {
          "system_turn_start": "<|im_start|>",
          "turn_start": "<|im_start|>",
          "label_start": "<|label|>",
          "end_of_turn": "<|im_end|>\n",
          "end_of_name": "\n",
      }
      cls.suffix = (
          cls.special_tokens["end_of_turn"]
          + cls.special_tokens["turn_start"]
      )
      cls.label_suffix = (
          cls.special_tokens["end_of_name"]
          + cls.special_tokens["turn_start"]
      )
  
imports: import json
  import os
  import random
  from functools import partial
  import pytest
  from nemo.collections.nlp.data.language_modeling.megatron.gpt_sft_chat_dataset import GPTSFTChatDataset, get_prompt_template_example
  from nemo.collections.nlp.modules.common.tokenizer_utils import get_nmt_tokenizer
label_desc: Use image node_id 1 for calling the TestDifferentGPTSFTChatDataset obj's underlying member method code with example usage: obj.setup_class(cls) without return types