The runtime of unittests
As there were some complains about the runtime of the unit-tests by @example, we should probably discuss how to deal with those.
Personally I am fine with a runtime of ~5min, but this of course depends on hardware and style of working. Also using e.g. Valgrind increase the runtime to currently ~30min. Still I don't think we should remove working test-cases on which people spend time to implement just because they take time to run. So I would suggest to split the unit-tests in a "quick" and a "long" category such that people without time and/or without fast hardware can run a reduced subset of the tests (e.g. all unit test which typically require less than 0.5s)?