code: def on_validation_epoch_end(self, trainer, model, unused=None):
      print("A val epoch ended.")
      self.validation_epoch_end_counter += 1
  
file_path: SynapseML/deep-learning/src/test/python/synapsemltest/dl/test_deep_vision_model.py
imports: import os
  import random
  from os.path import join
  import numpy
  import torch
  from PIL import Image
  from pytorch_lightning import Trainer
  from pytorch_lightning.callbacks import Callback
  from torch.utils.data import DataLoader, Dataset
  from synapse.ml.dl import *
label_desc: Use image node_id 6 for calling the MyDummyCallback obj's underlying member method code with example usage: obj.on_validation_epoch_end(trainer, model, unused) without return types