Suppose I'm making an algorithm that identifies the subject of a picture. It could be anything that a computer doesn't do that well, but I'm not expecting to get the right answer every time - 80% is fine. Suppose further, that the accuracy of the intermediate steps was also somewhat fuzzy. Is there a way to incorporate unit tests?

The option that immediately comes to mind is to add 1 to a tally and every time a 'test' passes, increment the tally. When that finishes, divide by the total and test 'passes/tests > 0.8', but that seems kludgey.

EDIT: Thank you all for your kind words and well-reasoned responses. My particular problem, while fuzzy, has nothing to do with pictures, and I'm currently getting about 80% pass. The short term value for me in a testing scheme would be knowing whether small adjustments were more globally beneficial or catastrophic. Long term testing value should be obvious.