assertNotNull(descendingMap.comparator());
assertEquals(navigableMap_startExcluded_endExcluded.firstKey(),
descendingMap.lastKey());
assertEquals(navigableMap_startExcluded_endExcluded.firstEntry(),
descendingMap.lastEntry());
assertEquals(navigableMap_startExcluded_endExcluded.lastKey(),
descendingMap.firstKey());
assertEquals(navigableMap_startExcluded_endExcluded.lastEntry(),
descendingMap.firstEntry());