A Unit Testing evangelist? Me?

Well, not altogether surprising, given my professional background, "once a tester always a tester" and all that.
But unit testing is your friend, really it is ..:)

Latest example:
I'm writing my first (very) small feature.
Completed the coding and the testing, was almost ready to integrate it.
Then it turned out my new class was supposed to be processing a different type of message altogether.
Ohmigod.
Well, less ohmigod since the messages are quite alike.
so, a bit of refactoring, most of it find/replace type of thing...

But... but... how do I know it still works???
My beloved (see earlier post) unit tests of course! They still run, so I haven't broke anything major with this refactoring ...