set @old_dbug=@@global.debug_dbug;
set global debug_dbug='+d,auth_disconnect';
create user 'bad' identified by 'worse';
set global debug_dbug=@old_dbug;
drop user bad;
set global debug_dbug='+d,auth_invalid_plugin';
create user 'bad' identified by 'worse';
ERROR 2059 (HY000): Authentication plugin 'foo/bar' cannot be loaded: invalid plugin name
set global debug_dbug=@old_dbug;
drop user bad;