code: def test_training_step(self, trainer, batch):
      # Test training step. Return torch.Tensor.
      loss = trainer.training_step(batch, batch_idx=0)
      assert isinstance(loss, 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 6 for calling the TestCNNTransformerTrainer obj's underlying member method code with example usage: obj.test_training_step(trainer, batch) without return types