Scala, PlayFramework, Mockito, ExecutionContext null - scala

Question

Following this answer: https://stackoverflow.com/a/30806548/4496364
I use Play's ExecutionContext in my project.
Recently I needed to use Mockito to test some services in Play.
So, this is simplified version of it:
import scala.concurrent.{ Future, ExecutionContext }
import play.api.libs.concurrent.Execution.Implicits.defaultContext
case class Model(id: Int, name: String)
trait DAO {
def findAll(implicit ec: ExecutionContext): Future[List[Model]]
}
class Service(dao: DAO) {
def findAll: Future[List[Model]] = dao.findAll
}
Test:
import play.api.libs.concurrent.Execution.Implicits.defaultContext
// doesn't work when different ExecutionContext
// import scala.concurrent.ExecutionContext.Implicits.global
class FuturesTest extends PlaySpec with MockitoSugar with ScalaFutures {
"Service" should {
"return all future data" in {
val mockModel = Model(1, "name")
val mockDAO = mock[DAO]
when(mockDAO.findAll) thenReturn Future.successful(List(mockModel))
val service = new Service(mockDAO)
val futureData = service.findAll
whenReady(futureData) { data =>
data.map(_.name) must contain(mockModel.name)
}
}
}
}
Note the comment in test, i get a NullPointException when calling dao.findAll in the Service. At first I thought that Mockito can't handle Scala's Futures but I figured out that the ExecutionContext is the problem. Since I'm not a concurrency expert, can someone please explain why does this happen?

Answer 1

In case someone is looking, the answer was obvious...
import org.mockito.Matchers.any
..
mockDAO.findAll(any[ExecutionContext])
I wasn't familiar with how Mockito works, or with Scala implicits.
When you don't pass any[ExecutionContext] Scala will fill it with the implicit one from the test.