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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.
If there isn't one already, why not add a test case to see whether or not a solution correctly returns a new array, per the instructions? A few of the Java solutions I saw were destructive.