code: def testOneStepReplayBufferObservers(self):
      if tf.executing_eagerly():
          self.skipTest("b/123880556")
  
      env = tf_py_environment.TFPyEnvironment(
          driver_test_utils.PyEnvironmentMock()
      )
      policy = driver_test_utils.TFPolicyMock(
          env.time_step_spec(), env.action_spec()
      )
      policy_state_ph = tensor_spec.to_nest_placeholder(
          policy.policy_state_spec,
          default=0,
          name_scope="policy_state_ph",
          outer_dims=(1,),
      )
      replay_buffer = driver_test_utils.make_replay_buffer(policy)
  
      driver = dynamic_step_driver.DynamicStepDriver(
          env, policy, num_steps=1, observers=[replay_buffer.add_batch]
      )
  
      run_driver = driver.run(policy_state=policy_state_ph)
      rb_gather_all = replay_buffer.gather_all()
  
      with self.session() as session:
          session.run(tf.compat.v1.global_variables_initializer())
          _, policy_state = session.run(run_driver)
          for _ in range(5):
              _, policy_state = session.run(
                  run_driver, feed_dict={policy_state_ph: policy_state}
              )
  
          trajectories = self.evaluate(rb_gather_all)
  
      self.assertAllEqual(
          trajectories.step_type, [[0, 1, 2, 0, 1, 2, 0, 1]]
      )
      self.assertAllEqual(
          trajectories.observation, [[0, 1, 3, 0, 1, 3, 0, 1]]
      )
      self.assertAllEqual(
          trajectories.action, [[1, 2, 1, 1, 2, 1, 1, 2]]
      )
      self.assertAllEqual(
          trajectories.policy_info, [[2, 4, 2, 2, 4, 2, 2, 4]]
      )
      self.assertAllEqual(
          trajectories.next_step_type, [[1, 2, 0, 1, 2, 0, 1, 2]]
      )
      self.assertAllEqual(
          trajectories.reward,
          [[1.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0, 1.0]],
      )
      self.assertAllEqual(
          trajectories.discount, [[1.0, 0.0, 1, 1, 0, 1.0, 1.0, 0.0]]
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import numpy
  import tensorflow
  from tf_agents.bandits.environments import environment_utilities
  from tf_agents.bandits.environments import stationary_stochastic_py_environment
  from tf_agents.drivers import dynamic_step_driver
  from tf_agents.drivers import test_utils
  from tf_agents.environments import tf_py_environment
  from tf_agents.policies import random_tf_policy
  from tf_agents.replay_buffers import tf_uniform_replay_buffer
  from tf_agents.specs import tensor_spec
  from tf_agents.utils import test_utils
label_desc: Use image node_id 4 for calling the DynamicStepDriverTest obj's underlying member method code with example usage: obj.testOneStepReplayBufferObservers() without return types