I doubt that you can. There was a study a while back, and I apologize in advance because I do not have a link, that showed projects written with unittests took significantly longer to reach the market, but with significantly less bugs. However, overall time spend on the code was less. So conclusion was that unittests are a commitment to a long term goal of minimizing developer time, and the tradeoff is that it takes longer for the first version to be done.

That is, as far as I know, the only tangible evidence that unittests are good unless you need to get something out the door quickly (which sadly is most of it).

I'd argue that is not the main benefit of unittesting however. That is the way code is structured, and especially how dependencies are explicit, e.g. injected with constructor arguments.