class_docstr: Mock environment for testing.
code: def get_observation(self):
      observation = np.empty((self.screen_size, self.screen_size))
      return self.ale.getScreenGrayscale(observation)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from gym import core
  import numpy
  import tensorflow
  from tf_agents.environments import atari_preprocessing
label_desc: Use image node_id 3 for calling the MockEnvironment obj's underlying member method code with example usage: obj.get_observation() and returns: self