Yes, fair enough, I seem to have a small problem with Proper Nouns today. Call it a German moment, if you will.
It's not my field any more, but here's an example from when it was: I wrote some code to perform a particular Monte Carlo simulation. Within the code were a number of functions which performed specific numerical computations. They were deterministic, so I unit tested them as you might expect using known results computed by an alternate technique. I found bugs, I fixed them.
However, the core function of the program, the simulation itself, I did not and could not know the "correct" result of, as it was a numerical simulation using pseudo-random numbers (so repeatable, but possibly repeatably wrong).
I had no other way of generating a specimen set of results. So, how was I supposed to test it? If you can offer a practical solution, I'll be impressed. I'm expecting some more hand-waving and hubris, however.