I have updated the testing gamemode to Gmod 13, i hope you don't mind that i used the logo we download from the server for the gamemodes logo.(let me know)
Installing:
Simply extract the zip file, and place the folder into \garrysmod\garrysmod\gamemodes\.
Using:
(http://i.imgur.com/zqu7PbB.jpg)
(http://i.imgur.com/9Qhz0Sa.jpg)
or type "gamemode slope_map_test" in console.
Download: http://www.mediafire.com/?i1in6ig1byfiw83
Now get out there and make some awesome maps :P