Play/Scala injecting Object into controller for testing

Question

I saw this thread Play/Scala injecting controller into test I have similar issue like this, but my issue is how to inject the object for testing the controller.

Controller

@Singleton
class ExampleCtrl @Inject() (dao: TestDAO) extends Controller {
//code here
   def testMethod = Action { request =>
       dao.exampleMethod()
       Ok(Json.obj("test" -> "test")
   }
 }

DAO

class TestDAO @Inject()(protected val provider: DatabaseConfigProvider){
  def exampleMethod()
}

Test

class ExampleCtrlSpec extends PlaySpec with MockitoSugar {
  val service = mock[TestDAO]//problem on injecting DatabaseConfigProvider
  val controller = new ExampleCtrl(service)
  //service has null value for DatabaseConfigProvider properties

  "testMethod()" should {
    "return JSON" in {
      when(service.exampleMethod) thenReturn "json data"
      val result: Future[Result] =
      controller.testMethod().apply(FakeRequest())
      .withJsonBody(JSON.json("""[{"test":"test"}]"""))
      contentAsString(result) mustEqual """[{"test":"test"}]"""
    }
  }
}

Answer 1

I solved the problem on the following way.

def testDAO (implicit app: Application) = {
    val app2testDAO = Application.instanceCache[TestDAO ]
    app2testDAO(app)
}
val controller = new ExampleCtrl(testDAO)

Answer 2

So I tried to reproduce the issue, but after fixing some issues that the IDE identified with the code (e.g. brackets missing), the test is passing.

problem on injecting DatabaseConfigProvider

I don't see any problem here, as the code is passing. From the coder's point of view, mock[TestDAO] doesn't actually instantiate a real TestDAO, but it creates something that looks like one (interface-wise), but doesn't actually contain any of the logic you wrote inside TestDAO. Therefore, the mock object also doesn't need the DatabaseConfigProvider to be injected.

service has null value for DatabaseConfigProvider properties

Because the service (your mock TestDAO) is a mock, this isn't a problem, since no logic will be using it. The only logic that your mock actually executes is here:

when(service.exampleMethod) thenReturn "json data"

When using mocks, you need to code the behaviour you want them to exhibit in the test, as you've done in the snippet above.

If you want to run any of the DatabaseConfigProvider methods, perhaps you need to:

• create one directly (e.g. val myProvider = [new] DatabaseConfigProvider(...)),
• move the mocking one level out, so that you have a real controller, a real TestDAO and a mock DatabaseConfigProvider (something like val controller = new ExampleCtrl(new TestDAO(mock[DatabaseConfigProvider]))), or
• write a different kind of test all together.