@Test
public void testHigherEntry() {

    IncrementalSortMap<Integer, String> map = map5();
    Map.Entry e1 = map.higherEntry(three);
    assertEquals(four, e1.getKey());
    Map.Entry e2 = map.higherEntry(zero);
    assertEquals(one, e2.getKey());
    Map.Entry e3 = map.higherEntry(five);
    assertNull(e3);
    Map.Entry e4 = map.higherEntry(six);
    assertNull(e4);
}