docstr: Test that a trajectory suffix has the correct observations.
code: def test_trajectory_suffix_observations(self):
      """Test that a trajectory suffix has the correct observations."""
      tr = rl_task.Trajectory(observation=0)
      for obs in range(1, 6):
          self._extend(tr, new_observation=obs)
      tr_suffix = tr.suffix(length=4)
      self.assertEqual(
          [ts.observation for ts in tr_suffix.timesteps], [2, 3, 4]
      )
      self.assertEqual(tr_suffix.last_observation, 5)
  
imports: import os
  from absl.testing import absltest
  import gym
  import numpy
  from trax import test_utils
  from trax.rl import task
label_desc: Use image node_id 8 for calling the TaskTest obj's underlying member method code with example usage: obj.test_trajectory_suffix_observations() without return types