code: def test_add_time_step(self):
      t = trajectory.Trajectory()
      t.add_time_step(observation=1, done=True)
  
      # Test that the trajectory is now active.
      self.assertTrue(t.is_active)
  
      added_t = t.last_time_step
      self.assertEqual(1, added_t.observation)
      self.assertTrue(added_t.done)
      self.assertIsNone(None, added_t.raw_reward)
      self.assertIsNone(None, added_t.processed_reward)
      self.assertIsNone(None, added_t.action)
  
      self.assertEqual(1, t.num_time_steps)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  import numpy
  from tensor2tensor.envs import time_step
  from tensor2tensor.envs import trajectory
  import tensorflow.compat.v1
  from tensorflow.compat.v1.io import gfile
label_desc: Use image node_id 2 for calling the TrajectoryTest obj's underlying member method code with example usage: obj.test_add_time_step() without return types