@Test
public void addingEqualSetDoesNothing() {

   addTwoElements(testSet);
   final LongHashSet equal = new LongHashSet(100);
   addTwoElements(equal);
   final HashSet<Long> equalCollection = new HashSet<>(equal);
   Assert.assertFalse(testSet.addAll(equal));
   Assert.assertFalse(testSet.addAll(equalCollection));
   assertContainsElements(testSet);
}