Port to new dune_add_test syntax

test/CMakeLists.txt

@@ -18,12 +18,7 @@ set(TESTS
   targetspacetest
 )
 
-add_directory_test_target(_test_target)
-add_dependencies(${_test_target} ${TESTS})
-
 foreach(_test ${TESTS})
-  add_executable(${_test} ${_test}.cc)
-  target_link_libraries(${_test} ${DUNE_LIBS})
-  add_dune_ug_flags(${_test})
-  add_test(${_test} ${_test})
+  dune_add_test(SOURCES ${_test}.cc)
+  target_compile_options(${_test} PRIVATE -g)
 endforeach()