Zeroconf is a fragile subsystem and we need unit and e2e tests to prevent regressions in Aseba::Zeroconf.

There are three ways to incorporate Aseba::Zeroconf in event loops: threads, Qt, Dashel.

There are three zeroconf implementations that might be used by Aseba: avahi, dns-sd, umdns.

PRs #653 and #678 were early attempts at Aseba::Zeroconf unit testing.