TDD love it or hate it, a question for HN Users

Assuming you are making an effort to do TDD or at least create unit tests once happy with a library, model, controller or just a script.

What methods do you employ to make sure the above stays in sync with the unit test.

Im sure, im not the first person to think about this, yet there is not any "best practices" I can find.

At present, im thinking.

db containing:

hash_of_the_file

name_of_the_unit_test

Then built into the test, or called ( not sure yet )

A way to check the db to make sure the hash_of_the_file still matches that in the db. Otherwise fail.

Any thoughts, or links would be well recieved.