A Test Mode to Test You Champion Build

I've been thinking about this for a long time now: there should be a testing mode in which you choose a champion to test out how particular items work with them. This can be very useful to summoners who have just bought a champion, those who are struggling with a build, etc. Practicing with a champion takes a VERY long time indeed, and with a tremendous amount of skill. Even with the free champion rotation, you only get so much time to practice with one you don't have yet, and WAM! There come the new free champions. Now you won't be able to practice with that champion you continuously played without (possibly) an official build. Only until you BUY them will you be able to play them constantly and maybe make/find a decent build. Plus, sometimes in beginner bot games, you won't be able to finish you build because the game progresses so quickly. I think this test will help a bunch; here's how it will work: your champion will be placed in a mini arena with another champion of your choice. (You can even switch them during the game.) You can give commands to the enemy champion- remain idle, run and/or attack. You can even put items on the enemy champion to see how strong you stand against them with your build. Of course, you'll be able to buy whatever items tickle your fancy, and, obviously, see how your champion is effected by them. I think this is a really good idea for the near future because I believe it will help A TON of players and even myself. What do you guys think? Do you think this should be a thing? Are there some parts of this game mode you would change? Let me know so this idea can be super easy, fun, and essential as possible! Thank you for all the support!