assertTrue(set2.contains(k1));
assertFalse(set2.contains(k2));
assertTrue(set2.contains(k3));
// test removeAll:
set3.removeAll(set1);
assertTrue(set3.contains(k1));
assertFalse(set3.contains(k2));
assertFalse(set3.contains(k3));
assertEquals("size", 1, set3.size());
}