"I want to test a (legacy) system but it wasn't designed with testability in mind." Ugly advice: fall back to manual "unit tests" with a debugger, temporary pr

"I want to test a (legacy) system but it wasn't designed with testability in mind." Ugly advice: fall back to manual "unit tests" with a debugger, temporary printf or whatever you have at hand. Does this eat a lot of time? Yes. Is it grungywork? Yes. Why do it then? Basically to surface the real cost of poor testability.