I’m a mechanical engineer, not a software person, but I write a lot of (hopefully close to professional quality) code for my work. writing tests while in the beginning/middle of my development cycle has been the best change I’ve made in how I do things in quite a long time. Since I’m a self-taught amateur often working solo, its invaluable for helping me gain confidence that everything I’m doing is working correctly as I learn the language/libraries necessary for me to build each new program.
I’m not saying that you yourself have this attitude - but the “tests are for suckers, I just ship” crowd really grinds my gears because to me it says “ha! Why do you care about getting things right?”
Totally get where you’re coming from though, sometimes the expected behavior is trivial to verify or (in the case of GUIs) can be very difficult and not worth the effort to implement.