In addition to what I've read here in the comments (that mocks are inaccurate, etc) I'll say that mocks also tend to just be plain overly verbose, at least in m

In addition to what I've read here in the comments (that mocks are inaccurate, etc) I'll say that mocks also tend to just be plain overly verbose, at least in my stack. We do a lot of our heaviest testing on our usecase logic, which is almost all very imperative and calling the DB + 3rd party APIs in various ways. Mocked tests here tend to be many times as long as the actual implementation, grow with the size of the implementation, and also tend to break immediately if you change the internals of your code (because now new things are being called, or not being called). Having hundreds of such tests can make refactors and serving new requirements a lot more annoying. The little "trick" of using SQLite to speed up integration tests has also bit me multiple times. Turns out the various RDBMSes are not in fact, all the same, and the details start to matter a lot very quickly.