"Maybe you're using a library that is difficult to mock. Maybe most of your logic is happening at the db layer." At this point, your design is already screwed

"Maybe you're using a library that is difficult to mock. Maybe most of your logic is happening at the db layer." At this point, your design is already screwed and borderline-unmaintainable, so yeah, I guess unit tests won't help much. But when people talk about Doing it Right, usually they mean having a codebase that's loosely coupled enough that tests are relatively simple to write.