I shipped this a couple of days ago.
How it works:
- Save the app icon variations to Dropbox on OS X.
- Launch Iconica+, link to Dropbox (once) and choose the icons to test
- App displays the icons in a simulated home screen. Swipe to see the icons against different types of wallpapers (colors, contrasts).
No manual rounding of icons, or manual positioning icons against different backgrounds. It's fast and simple, encouraging more variations to be tested.
There's a longer version of the story of the app at: http://hboon.com/iconica-app-for-ios-test-compare-ios-logos/.