I am sharing this story because it is funny, in a sad way. And because I don't post enough bad things about myself. I also want to make it clear that this story is completely and utterly my own fault for not explaining in full what we were doing to the other guy.
A few days ago I was pairing with a new guy about some code that we had to write to generate word documents. We run into a piece of code that had fairly complex requirements. (string parsing & xpath, argh!)
I thought that this would be a good way to get the point of unit testing, since the other guy didn't get the all the edge cases when I explained them (about 7, IIRC). So we sat down and wrote a test, and we made it pass, and we wrote another test, and made it pass, etc. It was fun, it made it very clear what we were trying to achieve, etc. This post is not about the values of unit tests.
I asked him were the test was, his answer was: "I deleted it, we were finished with that functionality, after all." *
* Nitpicker corner: I went and hit myself on the head for being stupid, he had no way of knowing, because I didn't explain nearly enough. I did afterward, and then I wrote the tests again.