Unit Testing Is Hard For All The Right Reasons

Last week I started a little experimental software project whose primary purpose is to apply standard software development techniques diligently and with rigor. This means coming up with a rough "top level" design, strict interface bounds, blackbox construction, and unit testing each component fully. The requirements for the project were laid out by a third party so that developers' influence wouldn't introduce a conflict of interest (ie coding the path of least resistance). I'm currently working on one of the main components of the system. Having come up with a strategy for the design and implemented the pieces of this component, I wrote up some unit tests for each piece and found it quite a challenge to cover all possible scenarios. In fact, writing the test cases is, at least for these relatively simple classes, harder and more time consuming than writing the classes themselves! I've already reaped some benefits from it however. In the testing phase I found a couple of one-off bugs that I might not have detected so soon without testing.

To help me out, I read through the following links and got some great pointers:

A Dozen Ways to Get the Testing Bug in the New Year (Particularly good)
Top 12 Reasons to Write Unit Tests
JUnit Primer