I've been contemplating how to balance testable design using dependency injection with providing simple fixed public API. My dilemma is: people would want to do something like var server = new Server(){ ... } and not have to worry about creating the many dependencies and graph of dependencies that a Server(,,,,,,) may have. While developing, I don't worry too much, as I use an IoC/DI framework to handle all that (I'm not using the lifecycle management aspects of any container, which would complicate things further).

Now, the dependencies are unlikely to be re-implemented. Componentisation in this case is almost purely for testability (and decent design!) rather than creating seams for extension, etc. People will 99.999% of the time wish to use a default configuration. So. I could hardcode the dependencies. Don't want to do that, we lose our testing! I could provide a default constructor with hard-coded dependencies and one which takes dependencies. That's... messy, and likely to be confusing, but viable. I could make the dependency receiving constructor internal and make my unit tests a friend assembly (assuming C#), which tidies the public API but leaves a nasty hidden trap lurking for maintenance. Having two constructors which are implicitly connected rather than explicitly would be bad design in general in my book.

At the moment that's about the least evil I can think of. Opinions? Wisdom?