Hi, I've found out about step-ca <https://github.com/smallstep/certificates> which has a ACME server implementation and could be used to write a self contained system test for certbot / ACME clients.
I didn't have much success packaging this for guix (it's written in go), perhaps someone more acquainted with the go-build-system could look at this direction? Having automated tests for certbot-service-type seems a worthwhile endeavor. Cheers, Bruno
