To test your design, use Flawless. Flawless works with the iOS Simulator, which mimics iOS devices and runs your code so that you can put your app through its paces. From the interface you’ll be able to compare your mockups to spot any differences between design and implementation.
You’ll also be able to use Split and Overlay modes to see how accurate implementation is. If any element of your design is even slightly pixelated or displaying the wrong shade, Flawless will pick up on it.