code: def validation_step(self, batch, batch_idx):
      loss = self(batch).sum()
      self.log("valid_loss", loss)
  
imports: import math
  from typing import Union
  import pytest
  import torch
  import pytorch_lightning
  from pytorch_lightning import LightningModule, Trainer
  from pytorch_lightning.trainer.states import RunningStage
  from torch.utils.data import DataLoader, Dataset
label_desc: Use image node_id 4 for calling the BoringModel obj's underlying member method code with example usage: obj.validation_step(batch, batch_idx) without return types