In fairness, I believe there exist code bases with a fragmented, poor design and lots of unit tests. I would place the blame with the programmer's design skill

In fairness, I believe there exist code bases with a fragmented, poor design and lots of unit tests. I would place the blame with the programmer's design skills, though, and not with scrupulously testable, loosely coupled modules. I do not believe that TDD is a replacement for good design skills at all, and it's easy TDD yourself into a poor design. Even strong TDD proponents like Uncle Bob admit as much [1]. However, I also believe that most good designs do happen to have the property of being easily unit testable, and if your code does not have that property, you should take pause. [1] http://www.infoq.com/interviews/coplien-martin-tdd http://www.infoq.com/interviews/coplien-martin-tdd, point 5 in the transcript