code: def test_extend(self):
      d = tf_metrics.TFDeque(3, tf.float32)
      self.evaluate(tf.compat.v1.global_variables_initializer())
  
      d.extend([1, 2, 3, 4])
      self.evaluate_last_func_if_graph_mode()
      self.assertEqual(3.0, self.evaluate(d.mean()))
      self.assertEqual(tf.float32, d.mean().dtype)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from absl.testing import parameterized
  import tensorflow
  from tf_agents.metrics import tf_metrics
  from tf_agents.specs import tensor_spec
  from tf_agents.trajectories import trajectory
  from tensorflow.python.eager import context
label_desc: Use image node_id 8 for calling the TFDequeTest obj's underlying member method code with example usage: obj.test_extend() without return types