assert_eq('banana'.find('na'), 2)
assert_eq('banana'.find('na', 3, 1), -1)
assert_eq('aaaa'.find('a', 1, 1), -1)
assert_eq('aaaa'.find('a', 1, 50), 1)
assert_eq('aaaa'.find('aaaaa'), -1)
assert_eq('abababa'.find('ab', 1), 2)
assert_eq('abababa'.find('ab', 0), 0)
assert_eq('abababa'.find('ab', -1), -1)
assert_eq('abababa'.find('ab', -2), -1)
assert_eq('abababa'.find('ab', -3), 4)
assert_eq('abababa'.find('ab', 0, 1), -1)
assert_eq('abababa'.find('ab', 0, 2), 0)
assert_eq('abababa'.find('ab', -1000), 0)
assert_eq('abababa'.find('ab', 1000), -1)
assert_eq(''.find('a', 1), -1)

assert_eq('banana'.rfind('na'), 4)
assert_eq('banana'.rfind('na', 3, 1), -1)
assert_eq('aaaa'.rfind('a', 1, 1), -1)
assert_eq('aaaa'.rfind('a', 1, 50), 3)
assert_eq('aaaa'.rfind('aaaaa'), -1)
assert_eq('abababa'.rfind('ab', 1), 4)
assert_eq('abababa'.rfind('ab', 0), 4)
assert_eq('abababa'.rfind('ab', -1), -1)
assert_eq('abababa'.rfind('ab', -2), -1)
assert_eq('abababa'.rfind('ab', -3), 4)
assert_eq('abababa'.rfind('ab', 0, 1), -1)
assert_eq('abababa'.rfind('ab', 0, 2), 0)
assert_eq('abababa'.rfind('ab', -1000), 4)
assert_eq('abababa'.rfind('ab', 1000), -1)
assert_eq(''.rfind('a', 1), -1)