Hmmm.. I can't find any example in the current Hilary code base where we test test setting or clearing particular config values. (The preview processor tests do update the config as part of their test scaffolding, but—other than checking for error responses—they don't attempt to verify the actual configuration changes.)

* Am I missing something obvious? (Won't be the first time.;^)
* If not, is there a preferred pattern for these types of tests?

It does seem like this could be a lot of work for testing what is nothing but a static JavaScript object. (There is no actual code in the module under test.) Would it be better to focus the tests on the config API itself? That's where the code is, and there are already plenty of tests there to verify its operation.