docstr: Test that the shape of a to_np result grows after calling extend().
code: def test_trajectory_to_np_shape_after_extend(self):
      """Test that the shape of a to_np result grows after calling extend()."""
      tr = rl_task.Trajectory(observation=0)
      for _ in range(5):
          self._extend(tr)
      len_before = tr.to_np().observation.shape[0]
      self._extend(tr)
      len_after = tr.to_np().observation.shape[0]
      self.assertEqual(len_after, len_before + 1)
  
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 10 for calling the TaskTest obj's underlying member method code with example usage: obj.test_trajectory_to_np_shape_after_extend() without return types