How to mock a call-by-name argument (like getOrElse) using ScalaMock?

callbyname, mocking, scala

Solution

The trick is to use `Product` version of `onCall` method, convert the second argument to `() => String` and call it:

class CallByNameMockSpec extends Specification with MockFactory {

  trait ToBeMocked {
    def getOrElse(arg: Int)(orElse: => String): String
  }

  "Mocking functions with call-by-name arguments" should {
    "work" in {
      val m = mock[ToBeMocked]

      (m.getOrElse (_: Int)(_: String)).expects(101, *).onCall(_.productElement(1).asInstanceOf[() => String]())

      m.getOrElse(101)("result") must beEqualTo("result")
    }
  }

}

Problem

I'd like to be able to mock a return value of `getOrElse` method so that it returns what is passed as `orElse` call-by-name argument with ScalaMock ``` trait ToBeMocked { def getOrElse(arg: Int)(orElse: => String): String } ``` ScalaMock has to be used because of currying. Running this: ``` class CallByNameMockSpec extends Specification with MockFactory { trait ToBeMocked { def getOrElse(arg: Int)(orElse: => String): String } "Mocking functions with call-by-name arguments" should { "work" in { val m = mock[ToBeMocked] (m.getOrElse (_: Int)(_: String)).expects(101, *).onCall((x, y) => y) m.getOrElse(101)("result") must beEqualTo("result") } } } ``` throws an exception: ``` [error] ClassCastException: test.service.CallByNameMockSpec$$anonfun$1$$anonfun$apply$1$$anonfun$apply$3$$anonfun$apply$4 cannot be cast to java.lang.String (CallByNameMockSpec.scala:16) ```

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