Designing app icons for Mac is a tedious process because you have to export the icon at various sizes to match Apple’s specifications. If you want a drop shadow on your icon, you have to take extra care to make sure the shadow isn’t clipped.
I made this Sketch template to help make it easier. The artboards are already set up to export all the required sizes. Get it for free here:
This is the source file I used to create the app icon for Shotty.