Tests or Clean Code: You Pick

If you had to choose between clean code and untidy code that is covered by tests, which would you pick?

The more that I do TDD, the more I have come to realize a minor flaw: TDD optimizes for test coverage, at the potential expense of untidy code. It's entirely possible with TDD to end up with code that passes all the tests, yet is not particularly readable. Now, if the "Refactor" step is performed properly, this can mitigate the problem. But even with refactoring, TDD's baby-steps approach to solving a problem does not always produce the most readable code. Too often, we are focused only on passing the current test and we lose sight of the overall design (assuming, of course, that we have a design).

The classic alternative is to do some initial design work, code, then cover the code with tests. But one of the main arguments for TDD is that writing tests after the fact often gets neglected by lazy programmers. Then who is to say that the same thing won't happen with TDD? That is, the "Refactor" step can fall by the wayside just as easily.

The question, then, is what are you optimizing for?

If the "Refactor" step is neglected, TDD can lead to working, yet untidy, code. Upfront design can lead to clean code, yet you haven't proved that it works if you fail to cover it with tests afterwards.

If it came down to it, I would probably pick covered, messy code. The next developer to work in the code would be less likely to break my functionality if there are tests in place, even if it initially may be less readable.

Ideally, of course, there would be no need to make such a compromise in the first place. What are your thoughts? How can we avoid this?