We have a nice helper for ensuring that these are unset.  It is `with_config` and defined [here](https://github.com/dockyard/ember-appkit-rails/blob/master/test/support/generator_test_support.rb#L15-L28).

Example is [here](https://github.com/dockyard/ember-appkit-rails/blob/master/test/generators/bootstrap_generator_test.rb#L47-L51).