As you probably know, I work in the software engineering department of a scientific institution of Russian Academy of Sciences, and my research and area of interest is software engineering. According to tag cloud, the "software-engineering" tag has reached the popularity of the "fun" tag; it does demonstrate my inclination.
But it was today when I wrote my first unit test.
And I loved it. Seven hours of ceaseless coding, brains not involved. Framework that runs it, hack to build system that assembles test application, mock objects controlled by environment variables -- that's how a bash/perl application is unit-tested, and that's totally not interesting. However, it was fun. I discovered two bugs in my application just by writing some unit-tests. Otherwise, I would delay the work, when we would encounter them later.
Unit-testing and automated test systems development
My whole career was devoted to developing automated testing systems. I was totally aware of why the tests are needed--it was the source of my income, actually. But why I never wrote unit-tests?
The answer to this question is simple. We, testing systems developers, get tests for free.
Usually, when you develop a testing system, you have a customer, whose software will be the primary target of it. Most likely, this software has several versions. And these versions differ dramatically from the viewpoint of a tester: the next version has less critical bugs to detect than the previous one.
And here's the test data. Just load the stuff you are to test! And here they are: a lot of regression tests for your tools.
The tests are essentially for free: you don't even need to think of test cases: the comparison with testing previous version yields enough information to decide whether your release if OK. And if you have another level of indirection, such as "test each version under each major Linux distribution", then you're likely to satisfy any vendor with your level of QA.
So if you happen to purchase an automated testing system (or merely have it developed), ask developers what kind of testing they made. If they somehow happen to have no regression tests, then it means that something's really wrong there. Because having such tests for free is an opportunity experienced testers wouldn't miss.