spec/spec_helper.rb adds Chef::Config.reset in between each test, so you shouldn't need to worry about backing up Chef::Config since you're requiring spec_helper.

We don't reset Ohai::Config, but we generally stub out ohai in the unit tests.

This feels more like a functional test, and I wonder if using the existing TinyServer framework from the functional tests would be better than this new chef-zero pattern (I don't know personally).