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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.
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The reason is your code is mutating the input array, and because the control function uses it afterwards, it gets the wrong expected value.
@kamilalew get the expected value first or pass a copy to the user's function.