(Aside: I think this is something PGlite helps with if your in Postgres land)
In the company I work for we use real PostgreSQL in unit tests — it's cheap to start one at the beginning of a suite, load the schema and go, and then shut it down and discard its file store.
I keep thinking of moving that file store to tmpfs when run on Linux, but it's nowhere near the top of the performance improvements for the test suite.
So: no more mocks or subsitute databases with their tiny inconsistencies.
Admittedly I’m only talking about selects, inserts, updates, views, etc. not stored procedures. But having worked in codebases with far too many stored procedures in the past, I think there might be a marginal improvement.
For what it’s worth, I fully agree that the main problem with using store procedures is testability and debugability.