code: def test_observation_np(self):
      t = trajectory.Trajectory()
      ts = 5
      shape = (3, 4)
      for _ in range(ts):
          t.add_time_step(
              observation=np.random.uniform(size=shape), done=False
          )
  
      self.assertEqual((ts,) + shape, t.observations_np.shape)
  
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 5 for calling the TrajectoryTest obj's underlying member method code with example usage: obj.test_observation_np() without return types