First of all, all enterprise applications, like probably any application, are written in source code. The source code is arguably the most important part of our software project. It represents the application and all its functionality at its core and can be seen as the single source of truth of software behavior.

The project's sources are separated into code that runs on production and test code to verify the application's behavior. The technologies as well as the quality demands will vary for test and production code. In Chapter 7, Testing, we will deeply cover the technologies and structures of software tests. Apart from that chapter, the focus of this book lies on production code, which is shipped and which handles the business logic.