class_docstr: Mock environment for testing.
code: def step(self, action):
      reward = -1.0 if action > 0 else 1.0
      self.num_steps += 1
      is_terminal = self.num_steps >= self.max_steps
  
      unused = 0
      self.ale.screen_value -= 2
      return (self.get_observation(), reward, is_terminal, unused)
  
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 4 for calling the MockEnvironment obj's underlying member method code with example usage: obj.step(action) and returns: self,  reward,  is_terminal,  unused