There is something appealing about "it's just a file" (it really isn't; it has locks and a WAL), but I agree with you.

I think people are afraid to read the documentation for postgres. You can start it up in milliseconds. Fast enough and light enough to run one copy for every test case in your test suite, or whatever you're using it for. (mkdir /tmp/whatever; initdb -D /tmp/whatever --no-instructions -A reject -c listen_addresses= --auth-local=trust --no-sync -c fsync=off -c unix_socket_directories=/tmp/whatever -U postgres --no-locale; postgres -D /tmp/whatever) Now you have a test database that behaves exactly like production because it's exactly like production. (OK, turning fsync off makes it a lot faster than production, so be careful.)