When Binding was just shoving stuff into ivars it made it so that we could not construct an object with Class.new for the purpose of testing. That defeats the purpose of DI entirely. So, instead, class_eval an initialize method from inside Class.inject.
I'm frankly unsure why the tests pass with a separate Injector instance as the class methods all still use the Singleton. In any case, this should now protect against any bleed-over between tests as it resets the singleton before each one.