A couple of years ago a collegue recommended Data Binding with Windows Forms 2.0: Programming Smart Client Data Applications with .NET and i noticed that my code started to gravitate towards an Model-View-ViewModel architecture. Due to shortcomings and painful experiences i gave up on databinding and began to use Passieve View instead.
Passive View doesn’t work (well) with smart views so i decided to give M-V-VM another because i really wanted to leverage WPF’s rich support for databinding.
The key difference between M-V-VM and Passive View is, imho, the fact that the ViewModel is unaware of the View unlike Passive View where the Presenter knows about the (simple) View.
When we test a Presenter i notice that we end up writing interaction based tests (assertions on a mocked view) and when we test a ViewModel we end up writing state-based tests instead.