My experience with TDD is that it is very helpful from a design perspective because it gets you to think about the code before you write it. How is the API going to work? What should I name this method? As an industry we use to dedicate too much time to this (RUP, etc). Now, we don't think about it enough.
As far as actually improving code quality... not so much. For the money, I would much rather see an hour of functional test development rather than an hour of unit test development (and I put TDD in the unit test category). I think functional tests provide more value and our industry has put way too much emphasis on unit tests.
100% unit test coverage says nothing about code quality. 100% functional coverage does. Functional tests also tend to be less brittle – which is a nice bonus.
As far as actually improving code quality... not so much. For the money, I would much rather see an hour of functional test development rather than an hour of unit test development (and I put TDD in the unit test category). I think functional tests provide more value and our industry has put way too much emphasis on unit tests.
100% unit test coverage says nothing about code quality. 100% functional coverage does. Functional tests also tend to be less brittle – which is a nice bonus.