[CMake] Add a test target for test/.

All folders called test/ are automatically added to CTest
by Dune and should provide a test target. Currently it is
a bug that a directory directly below the module is
ignored. Adding the target makes us future-proof.


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@12769 2fb0f335-1f38-0410-981e-8018bf24f1b0

test/CMakeLists.txt

@@ -4,3 +4,5 @@ add_subdirectory("freeflow")
 add_subdirectory("geomechanics")
 add_subdirectory("implicit")
 add_subdirectory("material")
+
+add_directory_test_target(_test_target)