@Test
public void testGetCountOfDistinctKeys(){

    IndexedCollection<Car> collection = new ConcurrentIndexedCollection<Car>();
    KeyStatisticsIndex<String, Car> MANUFACTURER_INDEX = NavigableIndex.onAttribute(Car.MANUFACTURER);
    collection.addIndex(MANUFACTURER_INDEX);
    collection.addAll(CarFactory.createCollectionOfCars(20));
    Assert.assertEquals(Integer.valueOf(4), MANUFACTURER_INDEX.getCountOfDistinctKeys(noQueryOptions()));
}