code: def test_step(self, batch, batch_idx):
      # Here we just reuse the validation_step for testing
      return self.validation_step(batch, batch_idx)
  
imports: import pytorch_lightning
  import torch
  from pytorch_lightning.metrics.functional import accuracy
  from torch import nn
  from torch.nn import functional
  from torch.utils.data import DataLoader, random_split
  from torchvision import transforms
  from torchvision.datasets import MNIST
  from labml import lab, experiment
  from labml.utils.lightning import LabMLLightningLogger
label_desc: Use image node_id 5 for calling the LitMNIST obj's underlying member method code with example usage: obj.test_step(batch, batch_idx) and returns: self