When run via karma, all the tests are loaded into the same page.
This was causing a collision in the 'displayed' assertion dealing
with using viewportLoc.

The assertions are now in their own file, pulled in by tests that
need them.  Additionally, several tests which only set fb_width
and fb_height were correct to set viewportLoc as well.

Closes #392

Also-Authored-By: Martin André (github: mandre)