Dependency Injection — Expert Decisions

Expert decision frameworks for dependency injection choices. Claude knows DI basics — this skill provides judgment calls for when and how to apply DI patterns.

Decision Trees

Do You Need DI?

Is the dependency tested independently?
├─ NO → Is it a pure function or value type?
│  ├─ YES → No DI needed (just call it)
│  └─ NO → Consider DI for future testability
│
└─ YES → How many classes use this dependency?
   ├─ 1 class → Simple constructor injection
   ├─ 2-5 classes → Protocol + constructor injection