def test_mask(self):
     self.assertEqual(
         Months.mask(datetime(1999, 12, 31, 23, 59, 59, 999999)),
         datetime(1999, 12, 1, 0, 0, 0, 0))
 def test_mask(self):
     self.assertEqual(
         Months.mask(datetime(1999, 12, 31, 23, 59, 59, 999999)),
         datetime(1999, 12, 1, 0, 0, 0, 0)
     )