What is a good example of unit test over specification?

I'm working on chapter 8 of my upcoming book and I need to come up with a good example of over specification in unit tests, that leads to an unmaintainable test in the long run (fragile test). I have my ideas on how to show it, but I'd love to know what you consider an over specified test, that can be shown with a concise (or even a bit contrived) code example.

- How would you define test over specification?

- how would you show it?

- are there multiple kinds of over specification with different ways to tackle them?