How to test wpf PrismApplication overridden methods such as RegisterTypes

[MatthewJRyan]

This is probably a dumb question but in past versions (<=6 for instance) with a explicitly created bootstrapper we could unit test our bootstrapper class and its overridden methods in relative isolation.
i.e. in a test we could new up our bootstrapper class, call the createcontainer and registertypes methods and then test that the required types have been registered/whatever. just an example and probably not a good one, but for the sake of explanation of intent it will do.

So how do we do this in a V8 PrismApplication based wpf app? Admittedly I'm very new to unit testing and so struggling to figure this out.

I looked in the source to see how you do it but there is just a todo (here assuming I'm looking in the right place)

Is this a use case for the headless bootstrapper method of creating a Prism wpf Application?
Or am I simply going about this all wrong?