Problem: test_filter_with_supplemental_process_owner_gid fails

Solution: only set supgroup to a valid gid

tests/test_filter_ipc.cpp

@@ -122,8 +122,10 @@ void init_groups ()
     supgroup = group;
     notgroup = group + 1;
     for (int i = 0; i < ngroups; i++) {
-        if (supgroup == group && group != groups[i])
-            supgroup = groups[i];
+        if (supgroup == group && group != groups[i]) {
+            if (getgrgid (groups[i]))
+                supgroup = groups[i];
+        }
         if (notgroup <= groups[i])
             notgroup = groups[i] + 1;
     }

tests/testutil.hpp

@@ -78,8 +78,10 @@
 #include <unistd.h>
 #include <signal.h>
 #include <stdlib.h>
+#include <grp.h>
 #include <sys/wait.h>
 #include <sys/socket.h>
+#include <sys/types.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <net/if.h>