public V flushedEntryStored(final K key) {
        return flushedEntries.get(key);
    }
Retrieve the value that the store {@link KeyValueStore#flush() flushed} with the given key.

@param key the key
@return the value that was flushed with the key, or {@code null} if no such key was flushed or if the entry with this
key was removed upon flush
streams/src/test/java/org/apache/kafka/streams/state/KeyValueStoreTestDriver.java