diff -r 65f6fdfd34b6 -r d8807b6a636a src/test/java/org/apidesign/java4browser/Instance.java
--- a/src/test/java/org/apidesign/java4browser/Instance.java	Thu Sep 20 09:29:42 2012 +0200
+++ b/src/test/java/org/apidesign/java4browser/Instance.java	Mon Sep 24 09:35:00 2012 +0200
@@ -53,4 +53,17 @@
         GetByte i = new InstanceSub(7, 2.2d);
         return i.getByte();
     }
+    public static boolean instanceOf(boolean sub) {
+        Instance i = createInstance(sub);
+        return isInstanceSubOf(i);
+    }
+    private static boolean isInstanceSubOf(Instance instance) {
+        return instance instanceof InstanceSub;
+    }
+    private static Instance createInstance(boolean sub) {
+        return sub ? new InstanceSub(3, 0) : new Instance();
+    }
+    private static boolean isNull() {
+        return createInstance(true) == null;
+    }
 }