This is great example of unit tests, but I don’t think it’s comparable with OP’s scenario. Math laws are ‘fixed’ and well known, you can just write fixed tests

This is great example of unit tests, but I don’t think it’s comparable with OP’s scenario. Math laws are ‘fixed’ and well known, you can just write fixed tests to find the discrepancy between the laws and your implentation. Where OP’s point is about ‘startup business logics’, the ‘laws’ here are constantly changing all the time, which means you will constantly throw out most of your tests along the way.