Hi,

• input validation is boring, you should get rid of it. If not, then it's not tested thoroughly: if an user is crazy enough to pass in null instead of the expected data structure, {}, and {{}} should be tested as well as {{{}}}
• random tests should be done using a loop, or the appropriated decorator to replicate the same tests several times. -> boils down to "don't repeat yourself".
• the random tests should also test for empty arrays and null (if the validation stays)
• this kind of task has already been done. A lot. => I don't think it's worth the effort of creating a new kata for it.

Cheers