I've found tests very useful for refactoring. I can pretty much go wild, as long as the tests pass at the end. About bugs in production, after you find a bug w

I've found tests very useful for refactoring. I can pretty much go wild, as long as the tests pass at the end. About bugs in production, after you find a bug write a test that exercises that bug. Then make the test pass. That way, you're unlikely to ever have a regression on that bug. For browser-side UI tests, selenium is very useful.