docstr: Test the shape yielded by trajectory stream.
code: def test_trajectory_slice_stream_shape(self):
      """Test the shape yielded by trajectory stream."""
      obs = np.zeros((12, 13))
      tr1 = rl_task.Trajectory(obs)
      self._extend(tr1, new_observation=obs, done=True)
      task = rl_task.RLTask(
          DummyEnv(), initial_trajectories=[tr1], max_steps=9
      )
      stream = task.trajectory_slice_stream(max_slice_length=1)
      next_slice = next(stream)
      self.assertEqual(next_slice.observation.shape, (1, 12, 13))
  
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 21 for calling the TaskTest obj's underlying member method code with example usage: obj.test_trajectory_slice_stream_shape() without return types