In this series, we'll work through refactoring a messy .NET Core MVC web application with a lot of procedural code and no tests. When we're done, we'll have a more testable, object-oriented, extensible application, complete with unit tests and static code analysis wired up with a continuous integration loop with GitHub Actions. We'll cover topics like inversion of control via dependency injection, replacing conditionals with polymorphism, factory methods, sending messages between small objects, unit testing, naming, and much more!
What is Legacy Code?
“Code without tests is bad code. It doesn’t matter how well-written it is; it doesn’t matter how pretty or object-oriented or well-encapsulated it is. With tests, we can change the behavior of our code quickly and verifiably. Without them, we really don’t know if our code is getting better or worse.”
― Michael Feathers, Working Effectively with Legacy Code
Legacy code - code without tests - is everywhere. It is not unusual in practice to encounter entire applications with few or even no tests. It is perhaps just as common to find software with legacy tests that don't adequately test current software behavior.