I just finished set of shell scripts which test failover and replication using Slony-1 and PostgreSQL.
It's somewhat Debian specific (using pg_ctlcluster to control PostgreSQL instances), but other than that it should work on any platform. This is essentially codification of requirements for HA testing I had to do, and I hope that this automatic demonstration would be valuable to others to test their specific requirements. Without this throwaway model, I wouldn't be able to test production database failover, because there is just too much steps which had to be done in specific order.
So, my fascination with testing expanded from development to deployment.