@Test
public void testAdd() {

  HistoryMap hm = makeHistoryMap();
  Assert.assertTrue("Expected other HistoryMap result, got " + hm,
             (hm.size() == 3) &&
             hm.containsValue(s1) && hm.containsValue(s2) && hm.containsValue(s3));
  hm.add(s4);
  Assert.assertTrue("First should be gone, but got" + hm,
             (hm.size() == 3) &&
             hm.containsValue(s2) && hm.containsValue(s3) && hm.containsValue(s4));
}