I wonder if you don't want to create a few different suites:
 - General layout
 In this suite we should probably test the height of the header. I would like to ensure that the any change to the header height is expected. My feeling is that component geometry changes is the main risk of breaking applications layout.

It looks dumb as well but you may also consider checking the action button is on the left, title in the middle, and application logic buttons on the right.
Why ? 
Because we may test the invert with RTL when we will support it and I would like to make sure we don't regress.
(the normal words for rtl compatible things are to not think in terms of left/right but start/end)

Also a test to ensure that element inserted by the applications can not overlap each other would be nice as well.
I guess an application can always break the layout if it is really trying to, but if there is a simple way to check that app author mistakes wont break the layout that would be nice (for example a very long title should not overlap the right buttons).

 - Action button behavior
 - Application elements behavior