BOOST_CHECK_EQUAL ("hello_world", careful_string_filter("héllo_wörld"));
BOOST_CHECK_EQUAL ("hello_world", careful_string_filter("héllo_wörld"));
BOOST_CHECK_EQUAL ("hello_world_a", careful_string_filter("héllo_wörld_à"));
BOOST_CHECK_EQUAL ("hello_world", careful_string_filter("héllo_wörld"));
BOOST_CHECK_EQUAL ("hello_world", careful_string_filter("héllo_wörld"));
BOOST_CHECK_EQUAL ("hello_world_a", careful_string_filter("héllo_wörld_à"));