new_contents: import collections
  import os
  import tempfile
  import time
  import unittest
  
  import mock
  
  from chainer import serializers
  from chainer import testing
  from chainer import training
  
  
  class TestTrainerElapsedTime(unittest.TestCase):
  
      def setUp(self):
          self.trainer = _get_mocked_trainer()
  
      def test_elapsed_time(self):
          with self.assertRaises(RuntimeError):
              self.trainer.elapsed_time
  
          self.trainer.run()
  
          self.assertGreater(self.trainer.elapsed_time, 0)
  
      def test_elapsed_time_serialization(self):
          self.trainer.run()
          serialized_time = self.trainer.elapsed_time
  
          tempdir = tempfile.mkdtemp()
          path = os.path.join(tempdir, 'trainer.npz')
          serializers.save_npz(path, self.trainer)
  
          trainer = _get_mocked_trainer((20, 'iteration'))
          serializers.load_npz(path, trainer)
  
          trainer.run()
  
          self.assertGreater(trainer.elapsed_time, serialized_time)
  
  
  def _get_mocked_trainer(stop_trigger=(10, 'iteration')):
      updater = mock.Mock()
      updater.get_all_optimizers.return_value = {}
      updater.iteration = 0
      def update():
          updater.iteration += 1
      updater.update = update
      return training.Trainer(updater, stop_trigger)
  
  
  testing.run_module(__name__, __file__)
  
subject: Add tests for Trainer.elapsed_time