Single node batch test.md

class KafkaSinkBatchSuiteV2
...
  test("single node batch") {
    val topic = newTopic()
    testUtils.createTopic(topic)
    val rand = new Random()
    val data = Seq.fill(100000)(Row(topic, rand.nextInt().toString))

    val df = spark.createDataFrame(
      spark.sparkContext.parallelize(data),
      StructType(Seq(StructField("topic", StringType), StructField("value", StringType)))
    )

    df.write
      .mode(SaveMode.Append)
      .format("kafka")
      .option("kafka.bootstrap.servers", testUtils.brokerAddress)
      .option("topic", topic)
      .save()
  }
...