I have to agree with CPD, this is an annoying limitation. I came to upgrade my views to GXT3 (The production version) and immediately hit this problem: My View is dumb, it just lays out the Widgets and exposes them to the presenter via methods that return interfaces like HasClickHandlers and HasVisiblity. As CPD mentions, this means I don't have to unit test my view at all, I can leave it for integrations tests.
I am concerned with multiple view implementations, and applying this technique allows me too change the view; Take a look at the implementers of HasClickHandlers, all clickable widgets in GWT implement it, so I can switch out my Button for an Anchor, or TextArea or a Canvas etc etc.
As it stands I have 2 options: Change all the View interfaces to expose HasSelectHandlers or wrap the Sencha Widgets to implement interfaces, something I had to do with the previous version and was hoping I would not have to do in the new version.