Add a unit test system to dune-testtools
It might sound very meta, but we need proper unit testing in dune-testtools. This includes:
- unit testing with loads of asserts for all python modules
- cmake macro unit tests
I have started implementing the second a while ago. It can be enabled with cmake -DENABLE_MACRO_TESTS=1. The tests themself take a subfolder each and are found in dune/testtools/test/*. I propose to place the python uniy tests in ./python/test