I write tests for my own servers, via the ruby gem ServerSpec. It's generally something I let lapse over time, but I always ensure that I update the tests before I'm applying a distribution update.

Allowing myself to validate that a Wheezy installation of Debian has all the services running that I expect after I upgrade it to Jessie is very useful and reassuring.

I wrote a brief introduction to the process here:

https://debian-administration.org/article/703/A_brief_introd...