docstr: Make sure calling the backward function on Tacotron2's outputs does
  not error out. Following:
  https://github.com/pytorch/vision/blob/23b8760374a5aaed53c6e5fc83a7e83dbe3b85df/test/test_models.py#L255
code: def test_tacotron2_backward(self, n_batch):
      r"""Make sure calling the backward function on Tacotron2's outputs does
      not error out. Following:
      https://github.com/pytorch/vision/blob/23b8760374a5aaed53c6e5fc83a7e83dbe3b85df/test/test_models.py#L255
      """
      n_mels = 80
      max_mel_specgram_length = 300
      max_text_length = 100
  
      model = _get_tacotron2_model(n_mels).to(self.device)
      inputs = self._get_inputs(
          n_mels, n_batch, max_mel_specgram_length, max_text_length
      )
      mel_out, mel_out_postnet, gate_outputs, _ = model(*inputs)
  
      mel_out.sum().backward(retain_graph=True)
      mel_out_postnet.sum().backward(retain_graph=True)
      gate_outputs.sum().backward()
  
imports: from typing import Tuple
  import torch
  from parameterized import parameterized
  from torch import Tensor
  from torchaudio.models import Tacotron2
  from torchaudio.models.tacotron2 import _Decoder, _Encoder
  from torchaudio_unittest.common_utils import skipIfPy310, TestBaseMixin, torch_script
label_desc: Use image node_id 4 for calling the Tacotron2Tests obj's underlying member method code with example usage: obj.test_tacotron2_backward(n_batch) without return types