Running the GUI test on macOS buildbots is not straightforward, AFAIK. We'd need to have either the console logged in to the username that the tests are running under or, better, the buildbot would need to run in a virtual machine. We have had a chronic shortage of macOS buildbots anyway. Plus the automated tests aren't all that good at finding the nasty problems that pop up in the intersection of the user, IDLE, and macOS Tk; at the moment, there's no substitute for manual testing.