### Question:
Hibernate4MemcachedRegionFactory implements RegionFactory { @Override public NaturalIdRegion buildNaturalIdRegion(String regionName, Properties properties, CacheDataDescription metadata) throws CacheException { return new NaturalIdMemcachedRegion(regionName, new OverridableReadOnlyPropertiesImpl(properties, cacheProviderConfigProperties), metadata, settings, memcachedAdapter, hibernateCacheTimestamper); } Hibernate4MemcachedRegionFactory();  Hibernate4MemcachedRegionFactory(Properties properties); @Override void start(Settings settings, Properties properties); @Override void stop(); @Override boolean isMinimalPutsEnabledByDefault(); @Override AccessType getDefaultAccessType(); @Override long nextTimestamp(); @Override EntityRegion buildEntityRegion(String regionName, Properties properties,
                                          CacheDataDescription metadata); @Override NaturalIdRegion buildNaturalIdRegion(String regionName, Properties properties,
                                                CacheDataDescription metadata); @Override CollectionRegion buildCollectionRegion(String regionName, Properties properties,
                                                  CacheDataDescription metadata); @Override QueryResultsRegion buildQueryResultsRegion(String regionName, Properties properties); @Override TimestampsRegion buildTimestampsRegion(String regionName, Properties properties); static final int MEMCACHED_MAX_EPIRY_SECONDS; static final AccessType DEFAULT_ACCESS_TYPE; static final String REGION_EXPIRY_SECONDS_PROPERTY_KEY_PREFIX; static final String MEMCACHED_ADAPTER_CLASS_PROPERTY_KEY; static final String TIMESTAMPER_PROPERTY_KEY; static final Class<?> DEFAULT_TIMESTAMPER_CLASS; }### Answer:
@Test public void buildNaturalIdRegion() throws Exception { givenStart(); NaturalIdRegion naturalIdRegion = regionFactory.buildNaturalIdRegion("books#naturalId", properties, metadata); assertThat(naturalIdRegion.getName()).isEqualTo("books#naturalId"); assertThat(naturalIdRegion).isExactlyInstanceOf(NaturalIdMemcachedRegion.class); }