code: def test_tokenize(self):
      tokenizer = GPT2Tokenizer.load(
          self.tmp_dir.name, self.special_tokens_map
      )
  
      text = "lower"
      bpe_tokens = ["low", "er"]
      tokens = tokenizer.map_text_to_token(text)
      self.assertListEqual(tokens, bpe_tokens)
  
      input_tokens = tokens + [tokenizer.unk_token]
      input_bpe_tokens = [13, 12, 17]
      self.assertListEqual(
          tokenizer.map_token_to_id(input_tokens), input_bpe_tokens
      )
  
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 4 for calling the GPT2TokenizerTest obj's underlying member method code with example usage: obj.test_tokenize() without return types