When http://puu.sh/bK2yN.jpg is selected, I'd like for testplaying to also force the default skin, as what you see inside the editor isn't how it looks during gameplay as previous notes fade faster, stacks will, well, stack, and not being able to see hitbursts. I'm pretty sure the purpose of this option is to make it easier to map and mod while making sure everything is readable with the default skin, so not applying this for testplaying doesn't really make sense.
If you need to test the map "properly" (aka. can't play with default skin), you can just go out of editor and play it, just like a player would play the map.
If you need to test the map "properly" (aka. can't play with default skin), you can just go out of editor and play it, just like a player would play the map.