@Test
public void testLowerEntry() {

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