No, Settings/Configuration is a classic example of where using a Singleton horribly breaks testability, because you can't run multiple "application runs" in the same "test run" without completely exiting and rebuilding the app runtime environment.
I would go as far as to say that if you have to do multiple "application runs" in the same "test run", where these "application runs" require different configurations to have the test cover some specific scenario, then your code has larger problems than having the configuration in a singleton.