code: def gen_name(self, test_config, prefix):
      save_dir = "checkpoint_test_logs"
      tag = test_config["tag"]
      checkpoint_name = test_config["checkpoint_name"]
      file_name = f"_{tag}_{checkpoint_name}.log"
      return os.path.join(save_dir, prefix + file_name)
  
imports: import unittest
  import subprocess
  import os
  import re
  from .test_common import BaseTestCase
label_desc: Use image node_id 20 for calling the GPT2CheckpointTestCase obj's underlying member method code with example usage: obj.gen_name(test_config, prefix) and returns: os