It's never too late for tests

So you've inherited a pile of buggy, spaghetti code, and now you're supposed to add some new features. We've all been there. It's very easy to say, "The code is already bad, so I'm not going to make the new features any nicer" but you shouldn't. This is your pile of spaghetti now, so you should work to make it incrementally better.

One big step in making bad code better is adding tests (I'm a firm believer in writing the tests first, so you shouldn't have much untested code, but it doesn't always happen). I'm not suggesting you drop everything and add tests to make sure you get to X% code coverage. But, as you add new features, you'll find yourself digging through old code. As you touch different parts of the code, refactor them where needed and add some tests. It will make you more confident in that part of the code, make life easier for yourself, and it will probably uncover some problems that you didn't know existed (and that have probably been there for a long time). A steady approach to testing will make any code better.