There is a class of problem where you know the goal, and code which produces the goal which you can test independently is demonstrably ok. Of course the next run with different parameters may well be wrong, but if they aren't on the goal-path you don't much have to worry.
I do sometimes code in this pattern. I have high confidence in charts from Google and Akamai about some data I have exposure to (a variant of the inputs unique to my situation not in their hands) and when the curves I make conform in general trend to the ones they make over the time series, I am pretty sure I have this right. If the critique is in the fine differences I do some differential on it. If the critique is in the overall shape of the curve, if mine is like theirs, why do you think I am so wrong?
I do sometimes code in this pattern. I have high confidence in charts from Google and Akamai about some data I have exposure to (a variant of the inputs unique to my situation not in their hands) and when the curves I make conform in general trend to the ones they make over the time series, I am pretty sure I have this right. If the critique is in the fine differences I do some differential on it. If the critique is in the overall shape of the curve, if mine is like theirs, why do you think I am so wrong?