code: def test_add_callback(self, dummy_handler, callbacks):
      dummy_handler.add_callback(callbacks)
      assert callbacks in dummy_handler.callbacks
  
imports: import os
  from collections import Counter
  import pytest
  import torch
  from pythae.models import AE, RAE_L2, VAEGAN, Adversarial_AE, Adversarial_AE_Config, AEConfig, RAE_L2_Config, VAEGANConfig
  from pythae.trainers import *
  from pythae.trainers.training_callbacks import *
label_desc: Use image node_id 1 for calling the Test_CallbackHandler obj's underlying member method code with example usage: obj.test_add_callback(dummy_handler, callbacks) without return types