Apache spark 返回数据流元组的火花测试基

我使用的是spark单元测试，我无法编译代码

  test("Testging") {
    val inputInsert = A("data2")
    val inputDelete = A("data1")
    val outputInsert = B(1)
    val outputDelete = C(1)

    val input = List(List(inputInsert), List(inputDelete))
    val output = (List(List(outputInsert)), List(List(outputDelete)))

    //Why doesn't it compile?? I have tried many things here.
    testOperation[A,(B,C)](input, service.processing _, output)
  }

我的方法是：

def processing(avroDstream: DStream[A]) : (DStream[B],DStream[C]) ={...}

在这种情况下“u”是什么意思