Single node streaming test.md

class KafkaSinkStreamingSuite
...
  test("single node streaming") {
    val input = MemoryStream[String]
    val topic = newTopic()
    testUtils.createTopic(topic)

    val writer = createKafkaWriter(
      input.toDF(),
      withTopic = None,
      withOutputMode = Some(OutputMode.Append))(
      withSelectExpr = s"'$topic' as topic", "value")

    try {
      for (i <- 0 until 10000) {
        input.addData(i.toString)
      }
      writer.processAllAvailable()
    } finally {
      writer.stop()
    }
  }
...