code: def get_activations(self, x, layer, batch_size):
      pass
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import logging
  import unittest
  import numpy
  from art.estimators.classification.classifier import ClassGradientsMixin, ClassifierMixin
  from art.estimators.estimator import BaseEstimator, LossGradientsMixin, NeuralNetworkMixin
  from tests.utils import TestBase, master_seed
label_desc: Use image node_id 4 for calling the ClassifierNeuralNetworkInstance obj's underlying member method code with example usage: obj.get_activations(x, layer, batch_size) without return types