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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.
How is this a suggestion?
Not a kata issue, you're mutating the input with pop, affecting the expected result. And remember to mark your post as having spoiler content.
Are you sure that's the input of that test? The log appears above the expected result. Another problem could be you're mutating the input.