def test_valid_format_returns_proper_timestamp(self):
     result = get_timestamp_from_file_name("some_file_20150404_234536.txt")
     self.assertEqual(datetime(2015, 4, 4, 23, 45, 36), result)
 def test_invalid_format_returns_none(self):
     result = get_timestamp_from_file_name("some_file_20150404_234df.txt")
     self.assertIsNone(result)