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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.
I think
assertEquals(0, Kata.grow(new int[]{0}));should be added to the tests. Or it should be in the description that the input will never be an array containing only 0.The method is receiving a reference to the array object, not a copy of the array. Any modifications made to the array will affect other parts of the code that have access to the original array. If you need to preserve the original array value, you can create a copy of the array within the method to prevent it from being modified.
Nice one!