Re: "Quality" is a structural attribute, not a bolt-on
Devs properly trained in TDD produce working code faster than without. You don't unit test constants, nor java setters & getters. You do write a test before you implement a branch in code execution.
For simply algorithms, yes, it is possible to create a golden dataset, and when the code passes it, it passes. Oh, wait. That's a different form of TDD!
But for complicated algorithms (and we are all guilty), state explosion makes this impossible. Worse, unless you have an advanced degree in mathematics, or a first-class undergraduate degree, you're going to miss things when you write tests before or after. (If you do, you are still going to miss things, but your training will keep you going back enough that your chance of committing bad code goes way, way down.)