Man, that is a lot but also thanks a lot.

• limit should be included. (considered it's done)
• add more edge cases. (considered it's done)
• snake_case usage. (done)
• specify the upper/lower limits. (What do you mean by this?)
• add more random test and more effective. (done)
• Improve the "complete solution". (Actually, because this is intended for beginners(7 or 8 kyu). I don't mind the limitation just up to 10**4. But still, I will change it later. It is good for future references.) (and do you mind if I use yours? because it is already in test cases ;-) )

Added. Thanks for the suggestion
I don't know what to do anymore because this is my first kata

If there are already same or similar katas with one that I want to make, How do I check them?