code: def test_forward(self, trainer, batch):
      # Test forward pass. Return torch.Tensor.
      output = trainer.forward(batch[0])
      assert isinstance(output, torch.Tensor)
  
imports: import pytest
  import torch
  import torch.nn
  from torch.utils.data import DataLoader, TensorDataset
  from kale.embed.image_cnn import SimpleCNNBuilder
  from kale.pipeline.base_nn_trainer import BaseNNTrainer, CNNTransformerTrainer, MultimodalNNTrainer
  from kale.predict.class_domain_nets import ClassNet
label_desc: Use image node_id 2 for calling the TestCNNTransformerTrainer obj's underlying member method code with example usage: obj.test_forward(trainer, batch) without return types