code: def test_forward(norm_vars, norm_means):
      layer = UtteranceMVN(norm_means=norm_means, norm_vars=norm_vars)
      x = torch.randn(2, 10, 80)
      y, _ = layer(x)
      assert y.shape == (2, 10, 80)
      y, ylen = layer(x, torch.tensor([10, 8], dtype=torch.long))
      assert (ylen == torch.tensor((10, 8), dtype=torch.long)).all()
  
imports: import pytest
  import torch
  from espnet2.layers.utterance_mvn import UtteranceMVN
label_desc: Use image node_id 2 for calling a global function with example usage: test_forward(norm_vars, norm_means) without return types