Unit tests - The benefit from unit tests with contract changes?

Question

Recently I had an interesting discussion with a colleague about unit tests. We were discussing when maintaining unit tests became less productive, when your contracts change.

Answer 1

I look at it this way, when your contract changes, you should treat it like a new contract. Therefore, you should create a whole new set of UNIT test for this "new" contract. The fact that you have an existing set of test cases is besides the point.