design-principles

Dependency injection makes code testable by enforcing explicit dependencies and boundary responsibility. You accept external collaborators as parameters rather than creating them, enabling easy mocking and implementation swapping.

Dependency inversion is a software design principle that decouples implementations by ensuring collaborators are injected. It relies on abstractions rather than concrete implementations to maintain testable and adaptable code.

You enforce explicit boundaries by identifying external collaborators and rewriting constructors and service functions to accept them rather than creating them internally, documenting expected behavior at boundaries.

You should accept dependencies rather than create concrete implementations when designing a new service to improve testability and flexibility, ensuring your business logic relies on injected abstractions.

Creating new collaborators inside business logic reduces testability because instantiating concrete implementations directly prevents easy mocking and swapping, tightly coupling your code to specific dependencies.

Yes, dependency inversion applies across service boundaries, constructors, and function signatures to ensure collaborators are injected and implementations are decoupled for maintainable code.