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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
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.
See if your program works on this input: [-12, -15]
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?
If you want to post an issue about bugs in the tests you have to tell where the tests are wrong.