code: def backward(self, reward, terminal):
      metrics = [np.nan for _ in self.metrics_names]
      self.memory.append(
          self.recent_observation, self.recent_action, reward, terminal
      )
      return metrics
  
imports: from __future__ import division
  import pytest
  import numpy
  from numpy.testing import assert_allclose
  from rl.memory import SequentialMemory
  from rl.core import Agent, Env, Processor
label_desc: Use image node_id 3 for calling the TestAgent obj's underlying member method code with example usage: obj.backward(reward, terminal) and returns: metrics