Pro's and Con's of unit testing after the fact

Question

I have a largish complex app around 27k lines. Its essentially a rule drive multithreaded processing engine, without giving too much away Its been partially tested as it\'s been

Answer 1

I think one of the biggest con of testing "after the fact" is that you will probably have a harder time testing. If you write code without tests, you usually don't have testability in mind and end up writing code that is hard to test.

But, after you spent this extra time writing tests and changing your code for better testability, you'll be much more confident about making changes, once you won't need a lot of time to debug and check if everything is ok.

Finally, you might find new bugs which weren't caught before, and spend some time fixing it. But hey, that's what tests are for =)