code: def test_PITSolver_forward(num_spk):
      batch = 2
      inf = [torch.rand(batch, 10, 100) for spk in range(num_spk)]
      ref = [
          inf[num_spk - spk - 1] for spk in range(num_spk)
      ]  # reverse inf as ref
      solver = FixedOrderSolver(FrequencyDomainL1())
  
      loss, stats, others = solver(ref, inf)
  
imports: import pytest
  import torch
  from espnet2.enh.loss.criterions.tf_domain import FrequencyDomainL1
  from espnet2.enh.loss.wrappers.fixed_order import FixedOrderSolver
label_desc: Use image node_id 1 for calling a global function with example usage: test_PITSolver_forward(num_spk) without return types