> with a mock you have to explicitly specify "when called with this return that".
Riiiight, no I've always hated that Mockito way of doing things.
I find wrapping a hashmap avoids the need for explicit when-this-then-that bindings, because a hashmap already does the expected behaviour natively.
You can even 'integrate' your tests as deeply as you like, all standing on top of your poor hashmap. I.e. Http tests with unit test speed.
var controller = new Controller(new Service(new Repo(new HashMap()))) controller.POST(...); assert(controller.GET(...));
EDIT: What I meant when I wrote that tests are not coupled to the underlying model/details is that with a mock you have to explicitly specify "when called with this return that". With an in memory database implementation you don't need to do anything, the code will just use the interface methods like "getX" or "saveY".