This was the most frustrating kata I've experienced so far on the site. Since it's pretty non-trivial to generate failing boards for row errors, column errors, or region errors, I suspect I won't be the only one who was stuck for a while totally unable to figure out what was causing some test failures on submission. I suggest these be added to the provided tests.

I also think region checking (which I'm not even sure is actually checked in the tests) makes this problem substantially more advanced than it's marked as being.