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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.
Sorry, but your code is returning the wrong answer, 3 is a prime number and -1 is not. And don't use caps like that please.
P.D.: after checking the javascript tests, it seems someone wrote some wrong error messages (the expected result was right, the message wasn't), fixed them.