### Question:
KafkaCache implements Cache<K, V> { @Override public void init() throws CacheInitializationException { if (initialized.get()) { throw new CacheInitializationException( "Illegal state while initializing cache for " + clientId + ". Cache was already initialized"); } if (localCache.isPersistent()) { try { checkpointFile = new OffsetCheckpoint(checkpointDir, 0, topic); checkpointFileCache.putAll(checkpointFile.read()); } catch (IOException e) { throw new CacheInitializationException("Failed to read checkpoints", e); } log.info("Successfully read checkpoints"); } localCache.init(); createOrVerifyTopic(); this.producer = createProducer(); this.consumer = createConsumer(); this.kafkaTopicReader = new WorkerThread(); try { this.kafkaTopicReader.readToEndOffsets(); } catch (IOException e) { throw new CacheInitializationException("Failed to read to end offsets", e); } this.kafkaTopicReader.start(); boolean isInitialized = initialized.compareAndSet(false, true); if (!isInitialized) { throw new CacheInitializationException("Illegal state while initializing cache for " + clientId + ". Cache was already initialized"); } } KafkaCache(String bootstrapServers,
                      Serde<K> keySerde,
                      Serde<V> valueSerde);  KafkaCache(KafkaCacheConfig config,
                      Serde<K> keySerde,
                      Serde<V> valueSerde);  KafkaCache(KafkaCacheConfig config,
                      Serde<K> keySerde,
                      Serde<V> valueSerde,
                      CacheUpdateHandler<K, V> cacheUpdateHandler,
                      Cache<K, V> localCache);  KafkaCache(KafkaCacheConfig config,
                      Serde<K> keySerde,
                      Serde<V> valueSerde,
                      CacheUpdateHandler<K, V> cacheUpdateHandler,
                      String backingCacheName,
                      Comparator<K> comparator); @Override Comparator<? super K> comparator(); @Override boolean isPersistent(); @Override void init(); @Override void sync(); @Override int size(); @Override boolean isEmpty(); @Override boolean containsKey(Object key); @Override boolean containsValue(Object value); @Override V get(Object key); @Override V put(K key, V value); @Override void putAll(Map<? extends K, ? extends V> entries); @Override @SuppressWarnings("unchecked") V remove(Object key); @Override void clear(); @Override Set<K> keySet(); @Override Collection<V> values(); @Override Set<Map.Entry<K, V>> entrySet(); @Override K firstKey(); @Override K lastKey(); @Override Cache<K, V> subCache(K from, boolean fromInclusive, K to, boolean toInclusive); @Override KeyValueIterator<K, V> range(K from, boolean fromInclusive, K to, boolean toInclusive); @Override KeyValueIterator<K, V> all(); @Override Cache<K, V> descendingCache(); @Override void flush(); @Override void close(); @Override void destroy();  }### Answer:
@Test(expected = CacheInitializationException.class) public void testDoubleInitialization() throws Exception { try (Cache<String, String> kafkaCache = createAndInitKafkaCacheInstance(bootstrapServers)) { kafkaCache.init(); } }