Sustainable testing

I tend to favour `call` for service objects instead of `run` as `run` implies more of a script or some __procedural__ work with side effects, potentially on a collection of objects. Especially if service object is working on a single object which mostly is the case i.e. `UserRegistration.new(user).call` makes more sense compared to `UserRegistration.new(user).run` although I wouldn't mind using `UserRecommendationMailer.new(users).run` as it is operating on a bunch of objects. Thoughts?