docstr: Test that ``T.TimeStretch`` fails gradcheck at 0
  
  This is because ``F.phase_vocoder`` converts data from cartesian to polar coordinate,
  which performs ``atan2(img, real)``, and gradient is not defined at 0.
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code: def test_timestretch_zeros_fail(self):
      """Test that ``T.TimeStretch`` fails gradcheck at 0
  
      This is because ``F.phase_vocoder`` converts data from cartesian to polar coordinate,
      which performs ``atan2(img, real)``, and gradient is not defined at 0.
      """
      n_fft = 16
      transform = T.TimeStretch(n_freq=n_fft // 2 + 1, fixed_rate=0.99)
      waveform = torch.zeros(2, 40)
      spectrogram = get_spectrogram(waveform, n_fft=n_fft, power=None)
      self.assert_grad(transform, [spectrogram])
  
imports: import unittest
  from typing import List
  import torch
  import torchaudio.transforms
  from parameterized import parameterized
  from torch.autograd import gradcheck, gradgradcheck
  from torchaudio_unittest.common_utils import get_spectrogram, get_whitenoise, nested_params, rnnt_utils, TestBaseMixin
label_desc: Use image node_id 19 for calling the AutogradTestMixin obj's underlying member method code with example usage: obj.test_timestretch_zeros_fail() without return types