Use stderr instead of stdout for warning.
diff --git a/Lib/test/test_signal.py b/Lib/test/test_signal.py
index ec7e06f..f458cdb 100644
--- a/Lib/test/test_signal.py
+++ b/Lib/test/test_signal.py
@@ -450,7 +450,7 @@
             if signal.getitimer(self.itimer) == (0.0, 0.0):
                 break # sig_vtalrm handler stopped this itimer
         else: # Issue 8424
-            sys.stdout.write("test_itimer_virtual: timeout: likely cause: "
+            sys.stderr.write("test_itimer_virtual: timeout: likely cause: "
                              "machine too slow or load too high.\n")
             return