Testing Retina images on an older Mac
Update 7.12.2020: Added info at the bottom about a UserDefaults setting you can use instead.
If you build iOS apps, you’re used to providing all icons and other images in @1x and @2x versions for older and Retina screens respectively (or rather @2x and @3x now). And it’s pretty easy to test if all those versions work or not, by starting the right iOS simulator and looking at it scaled to 100%.
If you work on Mac apps, you should also include @2x images for Retina Macs now; but if you’re like me, you might have treated that so far as something not urgent that can be done later…
When you do get around to that, if you don’t have any Retina Mac yet, you’ll quickly notice a problem: how do you test your app on a Retina screen? There’s no OSX simulator in Xcode, after all.