Write Tests Before Development

In my recent programming travels at work I have come across an increasing problem: Communicating the importance of testing to the project manager. Sometimes, oddly enough, the manager does not allocate time for testing in the development cycle, and simply accepts a spike solution as the final solution and asks for more features.

To a project group not accustomed to the methods of Extreme Programming, how does one communicate the effectiveness of the programming methodology to his or her peers? In my opinion it is simple, you just do it anyway.

Sure, the manager might moan about how it is taking you a little longer to get things "complete", but the difference is code that "somewhat provably works in all possible cases" versus code that "works in a small demo and might work in more cases". Writing tests first makes sense for a variety of reasons. First, it allows you to define the exact purpose of a method or function by testing different inputs on defined outputs. Every time I change or refactor some code in a class, I don't want to have to open up the GUI and click through different execution paths just to test some small method. Writing the tests first also allows you to double check a story with the "customer" who created the story (In my case the manager) and make sure the expected output is really what is expected. My final reason for writing the tests first is that you won't be tempted into not writing them later. A lot of times when we write code and build on it we can get the illusion that the building block classes that make up the outer level tested class work correctly, which might not necessarily be the case. If someone writes another api or class that utilizes an untested class, it opens up the door for new execution paths which can introduce new bugs.

Always test your code. Test first, and your life will be much easier later on in the development cycle. I can't stress it enough!