code: def training_step(self, batch, batch_idx):
      with torch.no_grad():
          out_bn = self.bn_layer(batch)
      self.bn_outputs.append(out_bn.detach())
      out = self.linear(out_bn)
      return out.sum()
  
file_path: pytorch-lightning/tests/parity_pytorch/test_sync_batchnorm_parity.py
imports: import torch
  import torch.nn
  from lightning.pytorch import LightningModule, Trainer, seed_everything
  from torch.utils.data import DataLoader, DistributedSampler
  from parity_pytorch import RunIf
label_desc: Use image node_id 3 for calling the SyncBNModule obj's underlying member method code with example usage: obj.training_step(batch, batch_idx) and returns: out