Temporary PostgreSQL instances for Go

tmppg locally spawns a new PostgreSQL database cluster for you to create databases in, mostly for tests. Since initializing a database cluster is relatively expensive, it can be done in a wrapper program: go run github.com/authenticvision/tmppg/cmd/wrapper@latest -- go test ./...

tmppg is a reimplementation of github.com/stapelberg/postgrestest with different opinions:

• Run postgres directly instead of via pg_ctl
• Pass config to postgres via CLI arguments instead of using a config file
• No Windows support
• An effectively worse startup check
• Use pgx instead of database/sql