[test.main_debug]

This can be used if the message of the DUNE_THROW(..., "failed bc of...")
macro is of importance. Just replace
    #include <dune/stuff/test/test_main.hh>
by
    #include <dune/stuff/test/test_main_debug.hh>
and run the test with `--gtest_catch_exceptions=0`. This change, however,
should not be committed and is intended for interactive debugging of tests
only!