* You're just describing arranging the test setup, which is independent of storage medium.

* Is your repository interface untyped?

* Depends on the fidelity of your fake, but generally I find FKs to be an antipattern these days.

* What are you checking primary keys FOR? Uniqueness is easy and I avoid more complex constraints and triggers.

* ... I'm beginning to suspect we have a difference in terminology. I'm not saying a mock. A typical DB fake would be array or hash table backed in memory. So an insert is "real" and an update or delete would be too.

* Well, sure, but I can get 95% fidelity for 1% of the resources.