Needs random tests.

There are no random tests.

I don't know how to play Mahjong and I'm confused about what the criteria for a winning set is, looking at wikipedia confused me more because there seem to be so many different regional variants.

Is the formatting important? Are the tiles alway going to be sorted?

It would be useful if the tests told you the reason why a set was not a winning set.

Here's what I have worked out:
They are either 4 groups of 3 plus 1 group of 2, or 7 groups of 2
The groups of 2 must all be different.
The groups of 3 may be identical?
The groups of 3 are either a) triples or b) runs of 3 consecutive numbers

Is this everthing? Is this correct?

The kata also needs some random tests.