Huge interfaces are not how you do it. Little ones, each expressing a conceptual unit of the functionality. Loggable. MessageConsumer. Stuff like that, even if

Huge interfaces are not how you do it. Little ones, each expressing a conceptual unit of the functionality. Loggable. MessageConsumer. Stuff like that, even if it only wraps one method. Make each major subsystem into an object, connect to it through the mini-interfaces it provides, and test its consumers by stubbing those mini-interfaces, not the whole object.