Regev,
1) If you are asking for a custom client specifically for testing wz instead of opening the game to test functionality, it would take a painstakingly ridiculous level of effort to replicate the entirety of the game MapleStory in the extreme extent of writing support for each version, every wz change, and multi region support, and without these near impossible features it'd still be mostly useless to the majority of people. MapleStory is a niche market anymore.. I imagine accounting for all of the potential client errors for that is too far fetched. Especially if its just "kinda annoying" for you..
If you really want to test it without worrying about dc then continue to test MapleStory itself each time. Idk.
2) If you were asking for something more to the effect of a BannedStory clone, which reads from wz which has a white background, no login, doesn't dc, written for testing the x and y of.. where a hair style would show up top of an avatar.. positioning wouldn't (always) require testing the actual client (using convoluted trial and error is time consuming)
Sorry for the confusion, but I don't know what exactly is being asked.