IO and global state is also just inputs that can be part of arrange-act-assert. Instead of mocking your database call to always return "foo" when the word "SELECT" is in the query, insert a real "foo" in a real test database and perform a real query.

Again I've heard "but what if my database/table changes so rapidly that I need the mock so I don't need to change the query all the time", in which case you ought to take a moment to write down what you're trying to accomplish, rather than using mocks to pave over poor architectural decisions. Eventually, the query fails and the mock succeeds, because they were completely unrelated.

So far I've only seen mocks fail eventually and mysteriously. With setups and DI you can treat things mostly as a black box from a testing point of view, but when mocks are involved you need surgical precision to hit the right target at the right time.

I don't understand the "but what if my database/table changes so rapidly that I need the mock so I don't need to change the query all the time". Are they changing your database schema at runtime (not just software update time when you can do migrations)? Otherwise you should have a test helper that creates your entire database schema so that when it changes you can update the schema in one place and all tests are re-run against the new one. (you should also have some insert common test data helpers that are easy to update as needed should the new schema affect the changes)

I haven't seen mocks fail mysteriously. I've seen them fail often though because requirements change and instead of updating the callers (generally a small number) you end up with 200 tests failing and give up because updating all the tests is too hard. Mocks are always about implementation details - sometimes you have no choice, but the more you can test actual behavior the better.