Unit testing is not just about catching errors while you build the code, it's (and much more) about being able to catch errors at any time. Now, tomorrow, in 2

Unit testing is not just about catching errors while you build the code, it's (and much more) about being able to catch errors at any time. Now, tomorrow, in 2 weeks, by someone else trying to refactor something in 10 years from now. Refactoring without tests is a nightmare and people will avoid touching anything because of it. With time that results in piles of old crap layered one over the another, hack over the hack, as no one ever wanted to take the responsibility of untangling it and refactoring the core problems properly. Many things you can do without tests, but tests make it more approachable and less scary to try.