OK, so you decide to add tests to your code. That typically isn’t so easy. The odds are that your code wasn’t designed and/or implemented to be easily testable. That means you will have to make changes to it to make it testable without breaking any of it (this is usually called refactoring these days). But how can you quickly and easily tell if you’ve broken anything without that comprehensive set of fine-grained tests? Tricky.It’s even trickier than that. If you take the approach that you’ll write tests for all your code after you write the code, you have to go to extra effort to try and design/write the code to be testable.

Maintaining an adequate level of testing when writing tests after the code being tested takes time and planning. And if you have to do additional work to make your code testable… well… that sucks.

Writing tests before you write the code means that the code is testable by definition. If you work one test at a time, you reap even more benefit, as each test only requires incremental changes to code that you know is solid.

I’m curious–how many of you actually write the code to the tests?  Do you actually write or follow a functional or technical spec?  Or do we always, always fly by the seat of our pants?