This would really just be god mode (Ability in a custom lobby (/j z -c) obtained with /ability god) with extra features. It wouldn’t be worth making a new mode just to test out maps. Also, If you control most things, it’s hard to really put a sense into what exactly will happen. For example, how do you know you will get the [weapon]? During the actual game, you may not have the right amount of score, or its blocked by zombies, etc.
Also if you want to fully test, you can test solo or with friends in a private lobby (/j z -p). You can also read this post : Zombies Abilities and Gameplay Strategies