We work in a Java shop here and our web application uses an implementation of the MVP architectural pattern. Our manager comes from a .NET world, where he has been exposed to the MVVM design pattern. Our manager is advocating changes in our MVP implementation, including that the Presenters should be decoupled from (or loosely coupled to, depending on your interpretation) its Views via the Observer design pattern, in tradition with MVVM. I am more of the opinion that the Presenter and the View work together to achieve a common goal, and as such should be coupled.
Among the arguments brought up in support of the change is the ability to unit test Presenters. If the Presenters only see the views as Observers, the argument goes, then they can be more easily unit tested. But presenters strongly coupled to their views are not necessarily difficult to test. If the View uses the Humble View paradigm, then it can be mocked. And finally, testability should be a symptom of good design, not a driver for the design.
Another argument used by my manager in support of layering the Views and the Presenters is the supposed maturity of MVVM. As such, we should follow MVVM's teachings and adapt to its implementation of MVP. Correct me if I'm wrong, but MVVM imposes the (artificial) layering of views and presenters in order to facilitate its data bindings in controls.
Can you please help us see the light here? Why should we use a decoupled model and pay the price for it? I'm not seeing the benefit. Occam's razor says I need arguments to use decoupling, and testing doesn't seem to be one of them.
Clarification: What I'm really looking for with this question are the arguments that can tip the balance in favor of a presenter that doesn't know about its view and shoots events in the aether or in favor of a presenter that knows about its view(s) through more direct coupling, like a humble view interface or directly to the class. Note that presenters can easily serve multiple views with both loose and tight coupling. The difference is in the interface that the presenter talks to: with loose coupling, the presenter talks to listener classes (or an event bus representative), whereas with tight coupling, the presenter talks to the view interface.