Specs2's mockito cannot mock the class which have the function returns AnyVal, but this example can be passes.

SampleSpec.scala

import org.specs2.mutable._
import org.specs2.mock._

trait Dummy extends Any

case class V(s: String) extends AnyVal with Dummy

class A {
  def f: Dummy = new V("Hello")
}

class Sample extends Specification with Mockito {
    "Mockito" should {
        "mock A" in {
            val a = mock[A]
            a.f returns new V("hoge")
            a.f match {
                case V("hoge") => success
                case _ => failure
            }
        }
    }
}