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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.
you are mutating the input array, this is why the assertion messages are confusing. i patched the tests so that the message is computed before the function call. your code is incorrect though, you need to fix it. also note that mutating your input when you are not asked to is bad practice, and in this kata in particular it cannot work as sometimes you will need to add an element.