These days, it's fairly common for me to be tasked to make a change that actually breaks the prior spec. I know that one of the major ideas behind TDD is to have a suite that verifies all your changes didn't actually break anything, but what do you do when the change you need to do, by it's very nature, actually must break the unit test?
How to do Test Driven Development is a similar, related question but it is subtlety different from my question. In my case, I already have the test and the specification has changed. In that question, the OP does not have the test yet.