code: def testNumEpisodesObserverEpisodeTotal(self, batch_size, traj_len):
      single_trajectory = np.concatenate(
          [
              [ts.StepType.FIRST],
              np.repeat(ts.StepType.MID, traj_len - 2),
              [ts.StepType.LAST],
          ]
      )
      step_type = np.tile(single_trajectory, (batch_size, 1))
  
      traj = trajectory.Trajectory(
          observation=np.random.rand(batch_size, traj_len),
          action=np.random.rand(batch_size, traj_len),
          policy_info=(),
          reward=np.random.rand(batch_size, traj_len),
          discount=np.ones((batch_size, traj_len)),
          step_type=step_type,
          next_step_type=np.zeros((batch_size, traj_len)),
      )
  
      observer = driver_test_utils.NumEpisodesObserver()
      observer(traj)
      self.assertEqual(observer.num_episodes, batch_size)
  
file_path: agents/tf_agents/drivers/test_utils_test.py
imports: from absl.testing import parameterized
  import numpy
  from tf_agents.drivers import test_utils
  from tf_agents.trajectories import time_step
  from tf_agents.trajectories import trajectory
  from tf_agents.utils import test_utils
label_desc: Use image node_id 1 for calling the TestUtilsTest obj's underlying member method code with example usage: obj.testNumEpisodesObserverEpisodeTotal(batch_size, traj_len) without return types