I should try to get a #FuckingXcode tag going. Because fucking #Xcode.
Run a test suite, all the tests get green checkmarks next to them. Then write a test that fails. To debug the test, run just that one test. All checkmarks remain while you run that one test, despite others not running. If you break another test, it looks like it still passes. If you use cmd-opt-ctrl-g to rerun the last test set run, it LOOKS like they all pass, but they don't. Xcode keeps stale pass icons instead of removing or greying them out. If don't remember you're not running the entire suite… ¯\_(ツ)_/¯
Fucking Xcode.