SortedMap head = sm.headMap(toKey);
assertEquals(1, head.size());
assertEquals(true, sm.containsKey(first));
assertEquals(true, head.containsKey(first));
assertEquals(true, sm.containsValue(firstValue));
assertEquals(true, head.containsValue(firstValue));
assertEquals(true, sm.containsKey(second));
assertEquals(false, head.containsKey(second));
assertEquals(true, sm.containsValue(secondValue));
assertEquals(false, head.containsValue(secondValue));