code: def test_set_loss(self) -> None:
      my_loss = nn.BCELoss()
      loss_name = "my_loss"
      self.op.trainer.set_loss(my_loss, loss_name=loss_name)
      self.assertEqual(loss_name, self.op.trainer.configs.loss)
  
imports: import unittest
  import torchvision
  from pathlib import Path
  from shutil import rmtree
  from torch import nn
  from torch.optim import AdamW
  from torchvision import transforms
  from towhee.operator import NNOperator
  from towhee.trainer.training_config import TrainingConfig
  from towhee.data.dataset.image_datasets import PyTorchImageDataset
label_desc: Use image node_id 3 for calling the TrainerTest obj's underlying member method code with example usage: obj.test_set_loss() without return types