without that check, in theory our test runner will tolerate
a non-zero return value, like throwing or failing an assert,
which is not what we want....
guess these happenend to get in by forgetting to
add this check when switching a test from PLANNED to TEST
due to the new automatic string conversion in operator<<
the representation of objects has changed occasionally.
I've investigated and verified all those incidents.
the buildsystem will now pick up and link
all test cases according to the layer, e.g.
backend tests will automatically be linked
against the backend + library solely.
