### Question:
CompositeReadOnlyKeyValueStore implements ReadOnlyKeyValueStore<K, V> { @Override public long approximateNumEntries() { final List<ReadOnlyKeyValueStore<K, V>> stores = storeProvider.stores(storeName, storeType); long total = 0; for (ReadOnlyKeyValueStore<K, V> store : stores) { total += store.approximateNumEntries(); } return total < 0 ? Long.MAX_VALUE : total; } CompositeReadOnlyKeyValueStore(final StateStoreProvider storeProvider,
                                          final QueryableStoreType<ReadOnlyKeyValueStore<K, V>> storeType,
                                          final String storeName); @Override V get(final K key); @Override KeyValueIterator<K, V> range(final K from, final K to); @Override KeyValueIterator<K, V> all(); @Override long approximateNumEntries();  }### Answer:
@Test public void shouldGetApproximateEntriesAcrossAllStores() throws Exception { final KeyValueStore<String, String> cache = newStoreInstance(); stubProviderTwo.addStore(storeName, cache); stubOneUnderlying.put("a", "a"); stubOneUnderlying.put("b", "b"); stubOneUnderlying.put("z", "z"); cache.put("c", "c"); cache.put("d", "d"); cache.put("x", "x"); assertEquals(6, theStore.approximateNumEntries()); }
@Test public void shouldReturnLongMaxValueOnOverflow() throws Exception { stubProviderTwo.addStore(storeName, new NoOpReadOnlyStore<Object, Object>() { @Override public long approximateNumEntries() { return Long.MAX_VALUE; } }); stubOneUnderlying.put("overflow", "me"); assertEquals(Long.MAX_VALUE, theStore.approximateNumEntries()); }