I became a fan of Extreme Programming working on projects with Dan Krech where we would pair program, unit test and refactor mercilessly.
On subsequent open source projects of my own, I fell in love with test-driven development. PyTREX was the first program I wrote that was entirely test-driven (back in March 2001).
The original post was in the category: software_craftsmanship but I'm still in the process of migrating categories over.