The issue with our current approach is that we need to keep the bazel tests fairly coarse (e.g., one bazel test for dozens of python tests) to keep the overhead of starting postgres instances down.
We make temp instances of Postgres quickly by:
- avoiding Docker, especially on Mac
- keeping the data dir on tmpfs
- Disable initdb cleanup
- Disable fsync and other data integrity flags
- Use unlogged tables.
- Use sockets instead of TCP localhost.
For a test suite, it was 12x faster to call createdb with the same Postgres cluster for each test than than to create a whole new db cluster. The trick was to create a template database after loading the schema and use that for each createdb call.
For what it's worth, we use rules_nixpkgs to source Postgres (for Linux and Darwin) as well as things such as C and Python toolchains, and it's been working really well. It does require that the machine have Nix installed, though, but that opens up access to Nix's wide array of prebuilt packages.