[thom]

Absolutely right. If you’re lucky, those are areas where you can capture the complexity in some sort of policy or calculator class and use property based testing to cover as much as possible - that’s a level of unit testing I’m definitely on board with. Sometimes it’s enough to just trust that your functional tests react appropriately to different _types_ of output from those classes (mocked) without having to drive every possible case (as you might have seen done in tabular test cases). For example I have an app that tests various ways of fetching and visualising data, and one output is via k-means clustering. I test that the right number of clusters gets displayed but I would never test the correctness of the actual clustering at that level. Treat complexity the same way you treat external dependencies, as something to be contained carefully.