def test_checksum_len3(): assert luhn.checksum('383') == 3
def test_checksum_len1(): assert luhn.checksum('7') == 7
def test_checksum_len2(): assert luhn.checksum('13') == 5
def test_checksum_len13(): assert luhn.checksum('4346537657597') == 9
def test_checksum_len14(): assert luhn.checksum('27184931073326') == 1
def test_checksum_len4(): assert luhn.checksum('2827') == 3