Comment 2 for bug 1641727

General implementation approach: refactor the ModelAssertionBuilder class to be able to work in parallel or volume-isolation. Have a driver class with one MAB per volume. Run their state machines to the given terminal, then have the driver class collect up all the results.

One tricky bit is that we'd like the driver to also be state-driven, so I have to figure out how to make that manageable. (Perhaps by forwarding the MAB state transitions through the driver.)