code: def testListMean(self):
      test_list = [1, 2, 3, 4, 5]
      mean = self.metrics._get_list_mean(test_list)
      self.assertEqual(mean, 3)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  import logging
  import tempfile
  from absl.testing import absltest
  import apache_beam
  from apache_beam.testing.test_pipeline import TestPipeline
  from apache_beam.testing.util import assert_that
  from apache_beam.testing.util import equal_to
  import tensorflow.compat.v1
  from tensorflow_text.tools.wordpiece_vocab import utils
label_desc: Use image node_id 2 for calling the CalculateMetricsTest obj's underlying member method code with example usage: obj.testListMean() without return types