@Override
    public String toString() {
        return new StringJoiner(", ", TestOutputTopic.class.getSimpleName() + "[", "]")
                .add("topic='" + topic + "'")
                .add("keyDeserializer=" + keyDeserializer.getClass().getSimpleName())
                .add("valueDeserializer=" + valueDeserializer.getClass().getSimpleName())
                .add("size=" + getQueueSize())
                .toString();
    }
Verify if the topic queue is empty.

@return {@code true} if no more record in the topic queue.
streams/test-utils/src/main/java/org/apache/kafka/streams/TestOutputTopic.java