code: def test_frontend_backward(
      fs, frontend_conf, multilayer_feature, layer
  ):
      frontend = S3prlFrontend(
          fs=fs,
          frontend_conf=frontend_conf,
          download_dir="./hub",
          multilayer_feature=multilayer_feature,
          layer=layer,
      )
      wavs = torch.randn(2, 1600, requires_grad=True)
      lengths = torch.LongTensor([1600, 1600])
      feats, f_lengths = frontend(wavs, lengths)
      feats.sum().backward()
  
imports: import pytest
  import torch
  from packaging.version import parse
  from espnet2.asr.frontend.s3prl import S3prlFrontend
label_desc: Use image node_id 3 for calling a global function with example usage: test_frontend_backward(fs, frontend_conf, multilayer_feature, layer) without return types