code: def ax(self):
      return self._ax
  
imports: import pytest
  from unittest import mock
  from yellowbrick.base import Visualizer
  from yellowbrick.utils.wrapper import *
  from yellowbrick.exceptions import YellowbrickAttributeError, YellowbrickTypeError
  from sklearn.naive_bayes import MultinomialNB
  from sklearn.naive_bayes import GaussianNB
label_desc: Use image node_id 2 for calling the MockVisualizer obj's underlying member method code with example usage: obj.ax() and returns: self