Attempt to use defaultReturn to automatically set up return values to methods on mock which the return instance of the mock. See my question to specs2-user mailing list - https://groups.google.com/forum/#!topic/specs2-users/My86VN-NT80

FooSpec.scala

//scala 2.10.2
//"org.scalaz" %% "scalaz-core" % "7.0.3"
//"org.specs2" %% "specs2" % "2.1.1" % "test"
//"org.mockito" % "mockito-all" % "1.9.0" % "test"

import scalaz.State._
import org.specs2.mutable.Specification
import org.specs2.mock._

trait Builder {
  def setA(a: Int): Builder
  def setB(b: Int): Builder
  // ..
  def setZ(z: Int): Builder
}

case class Request(
  a: Option[Int],
  b: Option[Int],
  // ..
  z: Option[Int]) {
  private def m = modify[Builder] _
  def prepare: Builder => Builder = (for {
    _ <- m(s => a.fold(s)(s.setA))
    _ <- m(s => b.fold(s)(s.setB))
    // ..
    _ <- m(s => z.fold(s)(s.setZ))
  } yield {}).exec
}

//val validRequest: Gen[Request] = ...

class FooSpec extends Specification with Mockito { // with ScalaCheck
  "prepare sets the appropriate properties" ! { //Prop.forAll(validRequest)
    val req = Request(Some(10), None, Some(11))

//    val builder: Builder = mock[Builder].defaultReturn(builder) // forward reference
//    val builder: Builder = mock[Builder].defaultAnswer(_ => builder) // forward reference
//    val tempBuilder = mock[Builder]
//    val builder = tempBuilder.defaultReturn(tempBuilder) // NullInsteadOfMockException

    // Must set up each call...
    val builder = mock[Builder]
    builder.setA(any[Int]) returns builder
    builder.setB(any[Int]) returns builder
    // ..
    builder.setZ(any[Int]) returns builder

    // Run test
    val result = req.prepare(builder)

    // Note that this produces UnfinishedVerificationException
    // there was req.b.fold(no(builder).setB(any[Int]))(one(result).setB)
    there was req.a.fold(no(builder).setA(any[Int]))(i => one(result).setA(i))
    there was req.b.fold(no(builder).setB(any[Int]))(i => one(result).setB(i))
    // ...
    there was req.z.fold(no(builder).setZ(any[Int]))(i => one(result).setZ(i))
  }
}