In a discussion a couple weeks ago with Anarcat, we discussed how to begin getting test coverage in Aegir. There currently isn't much (if any) testing in any of the Aegir components currently, which can lead to regressions that can be hard to identify. Adding testing to the front-end is difficult, as we'd need to simulate the back-end. IIRC, testing any back-end component appears to require tests to be in place for hosting_save, so we'll probably want to start with that.
BTW, to bootstrap this, Koumbit is offering to host a testing sprint in Chicago. Please let us know if you're interested here: http://community.aegirproject.org/node/448.
Otherwise, I propose that we use this issue to coordinate a testing strategy.