Dependency injection - best practice for fully decoupled components?

Question

I want to use dependency injection (Unity) and at the moment I'm thinking about how to setup my project (it's a fancy demo I'm working on).

So, to fully decouple all components and have no more assembly dependencies, is it advisable to create an assembly ".Contracts" or something similar and put all interfaces and shared data structures there?

Would you consider this the best practice or am I on a wrong track here?

What I want to accomplish:

Full testability, I want all components as sharply decouples as possible and inject everything, no component will ever talk directly to a concrete implementation anymore.

Answer 1

The first and probably most important step is to program to interfaces, rather than concrete implementations.

Doing so, the application will be loosely coupled whether or not DI is used.

Answer 2

I wouldn't separate interfaces in other assembly. If you have to interact with something that is a part of your domain, why separate it? Examples of interfaces are repositories, an email sender, etc. Supose you have a Model assembly where you have your domain objects. This assembly exposes the interfaces, and implementations, obviously, reference Model in order to implement them.