Robert Douglass wrote:

Hi everyone,

in very recent history I was faced with a set of programming problems that I was having a seriously difficult time handling. The architecture of my upcoming Solr module had gotten away from me, and every effort I made to reel it in and bring it under control was leading to dead ends and broken code. The way that I finally got out of the mess was by installing the Simpletest module and writing test cases for the functionality I needed. The act of codifying the expected behavior of every unit of the module helped me get over the hump and write code that works. Furthermore, the more test cases I produced, the faster the development proceeded. Code began to write itself (almost).

So I've now written an article on unit testing and Simpletest: http://www.lullabot.com/articles/introduction-unit-testing

I want to thank Moshe, Rok, and all the others who have worked on this code for so long, with so little praise. I hope that now the mass of Drupal developers will start to wake up to the potential of writing test cases and dig in.

http://drupal.org/project/simpletest

-Robert I agree with Robert here... When you start getting a lot of functionality in a single module and start re-engineering it, simpletest is a life saver, just for catching your oversights.