So, I have to understand the tests of the new resolver before I can write new ones.
Looks like there are various helpers. There's the script fixture, which is a PipTestEnvironment. That's going to be what ends up executing the various pip commands. It looks to me like the kind of tests I want are a pretty straightforward translation into the existing idioms.
I don't know when I'll be up for actually doing the translation, but I'll try to get started in the next few days.
I'll also need to get rid of some of the existing tests, but that shouldn't be too difficult.
I'm going to try to wrap up, and by try to wrap up, I mean put in some more work on the other thing I've been messng with.
(Also, since I took a break from the virtual tabletop stuff, I've had some time to think, and concluded that I've pushed nox too far, so I'm looking into alternatives that would give me stuff like, parallel execution, and dependencies between stages. I've got some plans sketched out, and the migration should be an interesting couple of days, week, month...)