Unlicensed user passed along a link to a terrific article in Dr. Dobb's titled The Relationship Between Testability and Good Design. From that article:
If we've learned anything over the past 10 years, it is that unit testing is an essential discipline. Tests help us better reason about our code, and they form a regression bedrock that makes refactoring and feature addition much easier. There is, however, a very subtle effect of unit testing that few people discuss. There seems to be an eerily consistent connection between testability at the unit level and good design. Almost uniformly, code that is hard to test has design problems. When you fix the design problems, it becomes easy to test.
Can you do unit testing with Clarion? Absolutely! There are two frameworks available, our own ClarionTest and Mark Goldberg's just-released cwUnit.
Thanks for the article link, Geoff!