[dagw]

How is the algorithm supposed to know what the right thing to return is

Some times I have, for example, matlab code that I 'know' is right and want to verify that my C/Python/Julia... code does the same thing. So then I just call the matlab code, call the new code and check if they're the same.

Or I have a slow exact method and want to see if my faster approximation always gives an answer 'close enough' to the correct answer.