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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.
Tests aren't correct. They're omitting non-duplicate values.
Fix up grammar in the instructions.
Be consistent with the instructions and tests. The instructions and the test ask for different error messages.