Mark Shuttleworth at LinuxTag

It's actually quite easy to write white-box testsuites for parts of systems -- *if you do it when you write the code*. If you do it then, you *know* the edge cases you have to test in your coverage testcase, and you *know* the boundaries you want to wander up to in any fuzz tests -- so it's fairly easy to write them.

What's a total sod is trying to do the same when faced with a bunch of code you wrote ages ago and no longer remember anything about, or that you didn't write at all.