Avoid retrofitting unit tests
I was asked this a few days ago, should we spend time creating proper unit tests for our code?
The team in question already have a set of integration tests, but very few tests that qualify as unit tests.
My response was rambling and long, but it can be put down to the following statement: TDD is a design technique, not a testing technique. TDD, and especially test first, have the nice side affect of leaving tests as part of the process, which can be incredibly helpful when you are working with the code. But retrofitting tests? That tends to be a waste of time.
Writing a unit test before touching the code is absolutely the way to go, but going and adding unit tests, as a task of its own? I don't see the value in that.
If you have integration tests there, that tends to be good enough, and you will write unit tests when you change the code, so eventually you'll have enough unit tests ( eventually you will have enough unit tests on the hot spots ).