Summary and Quiz: Hexagonal Architecture—Decoupling External System

Chapter’s recap

In this chapter, we learned how to apply the SOLID principles to decouple external systems completely, leading to an application architecture known as the hexagonal architecture. We saw how this allows us to use test doubles in place of external systems, making our tests simpler to write, with repeatable results. This, in turn, allows us to test entire user stories with a FIRST unit test. As a bonus, we isolate ourselves from future changes in those external systems, limiting the amount of rework that would be required to support new technologies. We’ve seen how the hexagonal architecture combined with dependency injection allows us to support several different external system choices and select the one we want at runtime via configuration.

Quiz