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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.
So, it does work. And please, remember using spoiler flag next time when posting code.
There is a test with -1 and this code works, why do you say it doesn't? Have you tried it?