not exactly best practices, but definitely really clever :-)

Clever, did the same thing myself only I didn't notice the kata didn't distinguise between lower and upper case characters so I did a ternary check for it. Really should've read the kata more carefully. 👍

My solution has five lines and still fast :P

Check my solution guys. Twice faster and have no cheats.

It should be mentioned in description that interpretor cells are unsigned

Yes, that test seems valid.

Sorry. My bad. How about that?

$this->revTest(playPass("Z", 130), "Z");

1.shift each letter by a given number but the transformed letter must be a letter (circular shift),

choose a text in capital letters including or not digits and non alphabetic characters

"z" is not a capital letter.

Please, add following test to Test Cases. There are a lot of fake solutions.
$this->revTest(playPass("z", 35), "I");

"Don't mutate the inputs" condition has not been met