--- jsr166/src/test/tck/TreeSubSetTest.java	2012/02/21 02:04:17	1.23
+++ jsr166/src/test/tck/TreeSubSetTest.java	2013/04/02 22:18:26	1.24
@@ -10,6 +10,7 @@ import java.util.Comparator;
 import java.util.Iterator;
 import java.util.NavigableSet;
 import java.util.SortedSet;
+import java.util.Set;
 import java.util.TreeSet;
 
 public class TreeSubSetTest extends JSR166TestCase {
@@ -1105,4 +1106,15 @@ public class TreeSubSetTest extends JSR1
         assertEquals(4, set.size());
     }
 
+    /**
+     * addAll is idempotent
+     */
+    public void testAddAll_idempotent() throws Exception {
+        Set x = populatedSet(SIZE);
+        Set y = new TreeSet(x);
+        y.addAll(x);
+        assertEquals(x, y);
+        assertEquals(y, x);
+    }
+
 }