code: def test_backward_not_leaf_in():
      layer = Stft()
      x = torch.randn(2, 400, requires_grad=True)
      x = x + 2
      y, _ = layer(x)
      y.sum().backward()
  
imports: import torch
  from espnet2.layers.stft import Stft
label_desc: Use image node_id 4 for calling a global function with example usage: test_backward_not_leaf_in() without return types