code: def test_lightweight_sinc_convolutions_forward():
      frontend = LightweightSincConvs(fs="16000")
      x = torch.randn([2, 50, 1, 400], requires_grad=True)
      x_lengths = torch.LongTensor([30, 9])
      y, y_lengths = frontend(x, x_lengths)
      y.sum().backward()
      assert y.shape == torch.Size([2, 50, 256])
  
imports: import torch
  from espnet2.asr.preencoder.sinc import LightweightSincConvs, SpatialDropout
label_desc: Use image node_id 3 for calling a global function with example usage: test_lightweight_sinc_convolutions_forward() without return types