PostgreSQL server is a single process that starts in under 100ms on a developer's laptop.

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.