embedded-postgres VS go-mutesting

So what can you do insted? For testing databases, setup a docker instance for tests (e.g. like in https://github.com/ardanlabs/service), or start an embedded-postgres daemon (see https://github.com/fergusstrange/embedded-postgres). For communication with external APIs, just pass the http.Client (either in context.Context or as a field on the struct). Then in tests, you can override the http.Client.Transport func.

There's also this interesting project, which embeds postgres into your binary: https://github.com/fergusstrange/embedded-postgres

This is down to nuance, but all databases are "file based" as they all write to files. But most of them require a separate process with lock coordination to get away from writer lock delays and ensure ACID, which includes Postgresql. Calling any version of pgl "embedded" is confusing because I see that being used to describe pgl databases which are run in a localhost mode with a single reader/writer client. Regardless, those still require a postgres process and access it over IP. For simplicity, if one uses a database by touching its files directly from the process accessing the database, then it's "embedded"; but then again I guess that semantic ship has sailed: https://github.com/fergusstrange/embedded-postgres so the point may be moot.

depending on the language you have chosen for your side project you might also be able to run postgresql in embedded mode here is the one for golang https://github.com/fergusstrange/embedded-postgres . There is similar solution for java as well.

I think this is the most up to date mutation testing library for Go: https://github.com/zimmski/go-mutesting