new_contents: from datetime import datetime
  import unittest
  
  from pypercube import time_utils
  
  
  class TestMetric(unittest.TestCase):
      def setUp(self):
          self.now = datetime(2012, 7, 6, 20, 33, 16, 573225)
  
      def test_yesterday(self):
          self.assertEqual(time_utils.yesterday(self.now),
                  datetime(2012, 7, 5, 20, 33, 16, 573225))
  
      def test_last_week(self):
          self.assertEqual(time_utils.last_week(self.now),
                  datetime(2012, 6, 29, 20, 33, 16, 573225))
  
      def test_start_of_month(self):
          self.assertEqual(time_utils.start_of_month(self.now),
                  datetime(2012, 7, 1))
  
      def test_floor(self):
          self.assertEqual(time_utils.floor(self.now, time_utils.STEP_10_SEC),
                  datetime(2012, 7, 6, 20, 33, 10))
          self.assertEqual(time_utils.floor(self.now, time_utils.STEP_1_MIN),
                  datetime(2012, 7, 6, 20, 33))
          self.assertEqual(time_utils.floor(self.now, time_utils.STEP_5_MIN),
                  datetime(2012, 7, 6, 20, 30))
          self.assertEqual(time_utils.floor(self.now, time_utils.STEP_1_HOUR),
                  datetime(2012, 7, 6, 20))
          self.assertEqual(time_utils.floor(self.now, time_utils.STEP_1_DAY),
                  datetime(2012, 7, 6))
          self.assertRaisesRegexp(ValueError, "is not a valid resolution",
                  time_utils.floor, self.now, 12345)
  
subject: Add unit tests for time_utils.