code: def setUpClass(cls):
      super().setUpClass()
  
      cls.n_train = 100
      cls.n_test = 10
      cls.x_train_mnist = cls.x_train_mnist[0 : cls.n_train]
      cls.y_train_mnist = cls.y_train_mnist[0 : cls.n_train]
      cls.x_test_mnist = cls.x_test_mnist[0 : cls.n_test]
      cls.y_test_mnist = cls.y_test_mnist[0 : cls.n_test]
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import logging
  import unittest
  import numpy
  from art.attacks.evasion.virtual_adversarial import VirtualAdversarialMethod
  from art.estimators.classification.keras import KerasClassifier
  from art.estimators.estimator import BaseEstimator
  from art.estimators.classification.classifier import ClassifierMixin
  from art.utils import get_labels_np_array
  from tests.utils import TestBase
  from tests.utils import get_image_classifier_tf, get_image_classifier_kr, get_image_classifier_pt
  from tests.utils import get_tabular_classifier_tf, get_tabular_classifier_kr, get_tabular_classifier_pt
  from tests.attacks.utils import backend_test_classifier_type_check_fail
label_desc: Use image node_id 1 for calling the TestVirtualAdversarial obj's underlying member method code with example usage: obj.setUpClass(cls) without return types