The Outside-In Approach

Outside-in is not just a testing strategy; it is a development approach. There is a misunderstanding that considers outside-in as a Mockist testing approach. You can do outside-in development using a classic testing approach. You can even do outside-in development without tests. Outside-in, from a systemic point of view, means focusing first on one of the most important aspects, the public interface, which for a system represents the communication with the external world. Remember that we see software as a system of systems? This is the reason for the quote of Alan Kay at the beginning of this lesson.

Furthermore, using this way of development fits incredibly well with the most popular IDE frameworks. Sketching the outside-in methods allows us to use quick shortcuts for almost every operation involving interface creation, class creation and method creation. It makes development mainly a matter of naming things and using the autocomplete functionality of the...