code: def setUp(self):
      vocab = [
          "l",
          "o",
          "w",
          "e",
          "r",
          "s",
          "t",
          "i",
          "d",
          "n",
          "lo",
          "low",
          "er",
          "low",
          "lowest",
          "newer",
          "wider",
          "<unk>",
      ]
      vocab_tokens = dict(zip(vocab, range(len(vocab))))
      merges = ["#version: 0.2", "l o", "lo w", "e r", ""]
      self.special_tokens_map = {"unk_token": "<unk>"}
  
      self.tmp_dir = tempfile.TemporaryDirectory()
      self.vocab_file = os.path.join(self.tmp_dir.name, "encoder.json")
      self.merges_file = os.path.join(self.tmp_dir.name, "vocab.bpe")
  
      with open(self.vocab_file, "w") as fp:
          fp.write(json.dumps(vocab_tokens))
      with open(self.merges_file, "w") as fp:
          fp.write("\n".join(merges))
  
file_path: texar/tests/data/tokenizers/gpt2_tokenizer_test.py
imports: import json
  import os
  import pickle
  import tempfile
  import tensorflow
  from texar.tf.data.tokenizers.gpt2_tokenizer import GPT2Tokenizer
  from texar.tf.utils.test import pretrained_test
label_desc: Use image node_id 1 for calling the GPT2TokenizerTest obj's underlying member method code with example usage: obj.setUp() without return types