The tests are fine, your function is returning a wrong answer. It's failing the second sample test, check your code.

No, you're wrong, and the test is fine:

• The first letter must be converted to its ASCII code.
• The second letter must be switched with the last letter

    v  v
l   ived
108 dvei
    ^  ^

See?

On the first test "A wise old owl lived in an oak" it's not "65 119esi 111dl 111lw 108dvei 105n 97n 111ka".
"lived" is "108devi" not "108dvei" when encrypted