The best way IMHO is to start simple and then add abstractions and interfaces over time. That will mean that, yes, when you come in to a project late there will

The best way IMHO is to start simple and then add abstractions and interfaces over time. That will mean that, yes, when you come in to a project late there will be lots of those... There are other practical reasons for using interfaces other than just "patterns" and "testing" though. Perf is one; you can avoid a lot of unnecessary mapping by being able to pass concrete types between modules when the receiver is accepting a shape instead of a concrete type...