code: def _substitute_stopwords(self):
      texts = ["The quick brown fox jumps over the lazy dog"]
  
      stopwords = [t.lower() for t in texts[0].split(" ")[:3]]
      aug_n = 3
  
      aug = naw.TfIdfAug(
          model_path=os.environ.get("MODEL_DIR"),
          action=Action.SUBSTITUTE,
          stopwords=stopwords,
      )
  
      for text in texts:
          self.assertLess(0, len(text))
          augmented_data = aug.augment(text)
          augmented_text = augmented_data[0]
  
          augmented_tokens = aug.tokenizer(augmented_text)
          tokens = aug.tokenizer(text)
  
          augmented_cnt = 0
  
          for token, augmented_token in zip(tokens, augmented_tokens):
              if token.lower() in stopwords and len(token) > aug_n:
                  self.assertEqual(token.lower(), augmented_token)
              else:
                  augmented_cnt += 1
  
          self.assertGreater(augmented_cnt, 0)
  
      self.assertLess(0, len(texts))
  
file_path: nlpaug/test/augmenter/word/test_tfidf.py
imports: import unittest
  import os
  import re
  from dotenv import load_dotenv
  import sklearn.datasets
  import nlpaug.augmenter.word
  import nlpaug.model.word_stats
  from nlpaug.util import Action
label_desc: Use image node_id 9 for calling the TestTfIdf obj's underlying member method code with example usage: obj._substitute_stopwords() without return types