write tests specific to universal lock files

[BurntSushi]

After #3831 lands, I should spend some time coming up with a bunch of test scenarios that specifically invoke the resolver without a marker environment. Pretty much all extant tests exercise a code path that invokes the resolver with a marker environment. So we should consider both adding new tests and exploring a way to leverage our existing test suite in a "universal" context.

Ref #3347

[BurntSushi]

I think this was closed by #4019.