### Question:
OptimisticEventStoreService implements EventStore { @Override public WritableEventStream createStream(String bucketId, String streamId) { return this.openStreamForWriting(bucketId, streamId, 0l); }  @Override ReadableEventStream openStreamForReading(String bucketId, String streamId); @Override ReadableEventStream openStreamForReading(String bucketId, String streamId, long version); @Override WritableEventStream createStream(String bucketId, String streamId); @Override WritableEventStream openStreamForWriting(
            String bucketId, String streamId, long version); @Override boolean existsStream(String bucketId, String streamId);  }### Answer:
@Test public void testCreateStream() throws Exception { cleanup(); WritableEventStream wes = eventStore.createStream(BUCKET_ID, "CREATED"); assertEquals(wes.version(), 0); testWriting(wes); assertEquals(BUCKET_ID, wes.bucketId()); assertEquals("CREATED", wes.streamId()); }