https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86272
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- Debug Mode does not use __gnu_debug::string it just disables the explicit instantation declarations in <string>, so that assertions in std::basic_string are turned on. To test __gnu_debug::string we really need a completely separate set of tests that include <debug/string> and use it explicitly as __gnu_debug::string. Given that it's probably never used by anybody (or they'd have noticed this bug) doing that is not a priority.
