tdd - Is there hard evidence of the ROI of unit testing?

Question

Unit testing sounds great to me, but I'm not sure I should spend any time really learning it unless I can convince others that is has significant value. I have to convince the other programmers and, more importantly, the bean-counters in management, that all the extra time spent learning the testing framework, writing tests, keeping them updated, etc.. will pay for itself, and then some.

What proof is there? Has anyone actually developed the same software with two separate teams, one using unit testing and the other not, and compared the results? I doubt it. Am I just supposed to justify it with, "Look it up on the Internet, everybody's talking about it, so it must be the right thing to do"?

Where is the hard evidence that will convince the laymen that unit testing is worth the effort?

Answer 1

Yes. This is a link to a study by Boby George and Laurie Williams at NCST and a another by Nagappan et al. I'm sure there are more. Dr. Williams publications on testing may provide a good starting point for finding them.

[EDIT] The two papers above specifically reference TDD and show 15-35% increase in initial development time after adopting TDD, but a 40-90% decrease in pre-release defects. If you can't get at the full text versions, I suggest using Google Scholar to see if you can find a publicly available version.