One of my weaknesses as a modern programmer is that I don't reallyunderstand how to do test driven development. I understand the basicideas of automated testing and unit testing and so on, and haveused them to reasonable effect every so often; where I fall down isunderstanding how to test things in more advanced and challengingcircumstances.

My current example of this is our ZFS spares handling system. Simplifiedslightly, the core program works by reading state information on all ofthe ZFS pools and their components (some