code: def test_substitute(self):
      for _ in range(10):
          aug = naa.VtlpAug(
              sampling_rate=self.sampling_rate, stateless=False
          )
          augmented_data = aug.augment(self.audio)
          augmented_audio = augmented_data[0]
          self.assertGreater(len(self.audio), len(augmented_audio))
  
file_path: nlpaug/test/augmenter/audio/test_vtlp.py
imports: import unittest
  import os
  from dotenv import load_dotenv
  import nlpaug.augmenter.audio
  from nlpaug.util import AudioLoader
label_desc: Use image node_id 2 for calling the TestVtlp obj's underlying member method code with example usage: obj.test_substitute() without return types