/** add throws NPE if offer does */
 public void testAddNPE() {
   Succeed q = new Succeed();
   try {
     q.add(null);
     shouldThrow();
   } catch (NullPointerException success) {
   }
 }
 /** add returns true if offer succeeds */
 public void testAddS() {
   Succeed q = new Succeed();
   assertTrue(q.add(two));
 }