code: def _get_mock_dataset(dataset_dir):
      """
      Creates the following directory structure:
          music
              fma
              fma-western-art
              hd-classical
              jamendo
              rfm
          noise
              free-sound
              sound-bible
          speech
              librivox
              us-gov
  
      Then, within each leaf subdirectory, adds a WAV file containing white noise @ 16KHz.
      """
      mocked_samples = {}
  
      seed = 0
      os.makedirs(dataset_dir, exist_ok=True)
      for subset, subdirs in _SUBSET_TO_SUBDIRS.items():
          subset_samples = defaultdict(dict)
          for subdir in subdirs:
              subdir_path = os.path.join(dataset_dir, subset, subdir)
              os.makedirs(subdir_path, exist_ok=True)
              file_name = f"{subset}_{subdir}.wav"
              file_path = os.path.join(subdir_path, file_name)
  
              data = get_whitenoise(
                  sample_rate=_SAMPLE_RATE,
                  duration=10.00,
                  n_channels=1,
                  dtype="float32",
                  seed=seed,
              )
              save_wav(file_path, data, _SAMPLE_RATE)
              subset_samples[file_name] = (data, file_path)
  
              seed += 1
          mocked_samples[subset] = subset_samples
      return mocked_samples
  
file_path: audio/test/torchaudio_unittest/prototype/datasets/musan_test.py
imports: import os
  from collections import defaultdict
  from parameterized import parameterized
  from torchaudio.prototype.datasets import Musan
  from torchaudio_unittest.common_utils import get_whitenoise, save_wav, TempDirMixin, TorchaudioTestCase
label_desc: Use image node_id 1 for calling a global function with example usage: _get_mock_dataset(dataset_dir) and returns: mocked_samples