def test_every_second_matches() -> None:
"""12131415 produces 4."""
assert rcaptcha.checksum_opposite(12131415) == 4
def test_all_match_halfway_ahead() -> None:
"""123123 produces 12."""
assert rcaptcha.checksum_opposite(123123) == 12
def test_easy_not_matching_halfway_ahead() -> None:
"""1221 produces 0, because every comparison is between a 1 and a 2."""
assert rcaptcha.checksum_opposite(1221) == 0
def test_one_match_halfway_ahead() -> None:
"""123425 produces 4, because both 2s match each other, but no other digit
has a match."""
assert rcaptcha.checksum_opposite(123425) == 4
def test_easy_halfway_ahead() -> None:
"""1212 produces 6: the list contains 4 items, and all four digits match
the digit 2 items ahead."""
assert rcaptcha.checksum_opposite(1212) == 6