code: def test_visualizations(self):
      # test that visualization doesn't error in grayscale and RGB settings
      (x_train, _), (_, _), (_, _) = self.mnist
      self.defence.visualize_clusters(x_train)
  
      x_train_rgb = convert_to_rgb(x_train)
      self.defence.visualize_clusters(x_train_rgb)
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import logging
  import unittest
  from keras.preprocessing.image import ImageDataGenerator
  import numpy
  from art.data_generators import KerasDataGenerator
  from art.defences.detector.poison import ActivationDefence
  from art.utils import load_mnist
  from art.visualization import convert_to_rgb
  from tests.utils import master_seed
label_desc: Use image node_id 16 for calling the TestActivationDefence obj's underlying member method code with example usage: obj.test_visualizations() without return types