code: def testFullLength(self):
      buf = py_metrics.NumpyDeque(
          maxlen=4, dtype=np.float64
      )  # pytype: disable=wrong-arg-types  # numpy-scalars
      buf.add(2)
      buf.add(3)
      buf.add(5)
      buf.add(6)
      self.assertEqual(4, buf.mean())
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from absl.testing import parameterized
  import numpy
  import tensorflow
  from tf_agents.metrics import py_metrics
  from tf_agents.trajectories import time_step
  from tf_agents.trajectories import trajectory
  from tf_agents.utils import nest_utils
label_desc: Use image node_id 2 for calling the NumpyDequeTest obj's underlying member method code with example usage: obj.testFullLength() without return types