alert should be considered a test failure unless overridden by the test case

test/src/main/java/org/jvnet/hudson/test/HudsonTestCase.java

@@ -24,6 +24,7 @@
  */
 package org.jvnet.hudson.test;
 
+import com.gargoylesoftware.htmlunit.AlertHandler;
 import com.gargoylesoftware.htmlunit.html.HtmlImage;
 import com.google.inject.Injector;
 import hudson.ClassicPluginStrategy;
@@ -1659,6 +1660,12 @@ public abstract class HudsonTestCase extends TestCase implements RootAction {
                 }
             });
 
+            setAlertHandler(new AlertHandler() {
+                public void handleAlert(Page page, String message) {
+                    throw new AssertionError("Alert dialog poped up: "+message);
+                }
+            });
+
             // avoid a hang by setting a time out. It should be long enough to prevent
             // false-positive timeout on slow systems
             setTimeout(60*1000);