@SuppressWarnings("WeakerAccess")
    public void awaitStoppedAndPurge() {
        kafka.awaitShutdown();
        log.debug("Removing log dir at {} ...", logDir);
        try {
            Utils.delete(tmpFolder);
        } catch (final IOException e) {
            throw new RuntimeException(e);
        }
        log.debug("Shutdown of embedded Kafka broker at {} completed (with ZK ensemble at {}) ...",
            brokerList(), zookeeperConnect());
    }
The ZooKeeper connection string aka `zookeeper.connect`.
streams/src/test/java/org/apache/kafka/streams/integration/utils/KafkaEmbedded.java