This will only get a permission defined error if not running as root.

ext/posix/tests/posix_errno_variation1.phpt

@@ -7,6 +7,7 @@ Francesco Fullone ff@ideato.it
 --SKIPIF--
 <?php 
         if(!extension_loaded("posix")) print "skip - POSIX extension not loaded"; 
+        if(posix_getuid()==0) print "skip - Cannot run test as root.";    
 ?>
 --FILE--
 <?php