Scala: Mocking and the Cake Pattern

Question

I\'ve been trying to adopt the Cake Pattern but I\'m having difficulties adapting to this programming styles, especially where unit tests are concerned.

Lets assume that

Answer 1

I have found a way to use Scalamock with Scalatest for the purpose of unit testing 'Cake Pattern' modules.

At first, I had many problems (including this one), but I believe the solution I present below is acceptable. If you have any concerns, please let me know.

This is how I would design your example:

trait VetModule {
  def vet: Vet
  trait Vet {
    def vaccinate(pet: Pet)
  }
}

trait PetStoreModule {
  self: VetModule =>
  def sell(pet: Pet)
}

trait PetStoreModuleImpl extends PetStoreModule {
  self: VetModule =>
  def sell(pet: Pet) {
    vet.vaccinate(pet)
    // do some other stuff
  }
}

The tests are then defined as following:

class TestPetstore extends FlatSpec with ShouldMatchers with MockFactory {

  trait PetstoreBehavior extends PetStoreModule with VetModule {

    object MockWrapper {
      var vet: Vet = null
    }

    def fixture = {
      val v = mock[Vet]
      MockWrapper.vet = v
      v
    }

    def t1 {
      val vet = fixture
      val p = Pet("Fido")
      (vet.vaccinate _).expects(p)
      sell(p)
    }

    def vet: Vet = MockWrapper.vet
  }

  val somePetStoreImpl = new PetstoreBehavior with PetStoreModuleImpl
  "The PetStore" should "vaccinate an animal before selling" in somePetStoreImpl.t1
}

Using this setup, you have the 'disadvantage' that you have to call val vet = fixture in every test you write. On the other hand, one can easily create another 'implementation' of the test, e.g.,

val someOtherPetStoreImpl = new PetstoreBehavior with PetStoreModuleOtherImpl