I've been having plenty of Swift 4 vs. Swift 3.1.1 issues. Great practice in both versions of Swift and building my own tests. Keep on swimming.

Swift 3: myString.characters.count
Swift 4: myString.count

Remember that Swift 4 String is collection of Characters, but Swift 3 is not. (see "string".characters) These plus other testing issues may block success.

Really like that if let for identifying a number 0...9!

See if your program works on this input: [-12, -15]

I'm pretty sure, that my code is working right. Sample tests are working right, but when i send attempt tests fails with error

Unfortunately for you there are no errors in the tests. Have you thought of possible edge cases? Have you look at the top of the page how many guys passed the kata? Don't you mutate the input?

Test fails with error "fatal error: Index out of range", but in xcode all works perfectly well with test data. So the only reason i see here is bug in tests

If you want to post an issue about bugs in the tests you have to tell where the tests are wrong.

Test is crushing on Swift. And it's not the only kata, that i couldn't finish cause of bugs in tests

Have same problem. Tests doesn't work, not code. But i have no idea how to fix this