This presentation explains how to easily test in an autonomous way, in a test bed, an application conceived with modular abstractions such as the “layer”. You will acquire fundamental knowledge about how to partitions into layers the concerns of the application. We will teach you the best practices regarding application architecture and modularity. We will demonstrate how to apply “top-down” as well as “test-driven” design techniques. You will learn how to correctly design the “velcro”, the visible interface of a module. In the same way, you will learn how to conceive a “fake” implementation, an efficient strategy to test a module in an autonomous way. Overall, you will learn how to design for testability and why we need a unit of modularity that goes beyond object.