I guess it depends a bit on what you work on. Lately I'm working on algorithm heavy stuff, then testing input=>output is much more valuable than if things run,

I guess it depends a bit on what you work on. Lately I'm working on algorithm heavy stuff, then testing input=>output is much more valuable than if things run, easier to consider edge cases when calling it directly etc. But if you make a crud app it's often more useful to test a flow. So depends. As for mocks I don't disagree, hence calling it worst case. What often works for me is separating the code. For instance if I call a function that first queries the db and then marshall that data into something, it's often easier to test it by splitting it. One function that queries, that one can test with some db fixtures or other setup. And then another that gets a model in and only does the pure logic and returns the result. Can then be tested separately. And then a third function which is the new one, that just calls the first and pass the result into the second. Can be boilerplaty, so again, depends.