Ranks can't be changed, the author doesn't decide the rank, and not a suggestion.

For each language:

• C# - This has 100 random tests, so that one is alright already.
• JavaScript - This only had five random tests, so I've increased it to 100.
• Ruby - This has no random tests, but an issue has been raised for that.

Definitely not 4kyu in my opinion but ranking it as 5kyu would be more than fair.

By the way, this was one of the hardest 6kyu Katas I have ever solved. I had to constantly console.log different stages of my code to verify what was actually going on as I coded my algorithm.