Future's .recover not getting called when Exception is thrown in Mockito unit test

Question

The following code returns a Future.

val findUserFuture: Future[Option[User]] = userRepo.findOne(userKeys) 

Then I process the Future

findUserFuture.flatMap {....}
.recover{...}

fineOne returns the Future and the Future wraps call to getOneById

def findOne(userKeys:UserKeys):Future[Option[User]] = {
    Future{
      //val loginInfo:LoginInfo = LoginInfo(userKeys.providerID,userKeys.authProvider)
      val userOption:Option[User] = getOneById(userKeys)
      userOption
    }
  }

I suppose that recover will be called if Future returned by findOne fails i.e. throws an Exception. So I am simulating that by making getOneById throw an exception.

when(mockUserRepository.findOne(userKeys)).thenReturn(Future(Some(user)))
      when(mockUserRepository.getOneById(userKeys)).thenThrow(classOf[RuntimeException]) //simulating database error

But the unit test doesn't throw an exception and the test proceeds using value Future(Some(User)).

I also tried throwing the exception from findOne - when(mockUserRepository.findOne(userKeys)).thenThrow(classOf[RuntimeException]) but the test case stops with the following two prints and the .recover of the Future is not called

java.lang.RuntimeException was thrown.
java.lang.RuntimeException

Answer 1

This findUserFuture: Future[Option[User]] or userRepo.findOne returns future, hence you need to return Future.failed in your mock. For ex.

when(mockUserRepository.findOne(userKeys)).thenReturn(Future(Some(user)))
when(mockUserRepository.getOneById(userKeys)).thenReturn(Future.failed(new RuntimeException("network failure"))

Find below complete working test to simulate your use case :

test("mock future test") {
    case class User(name: String)
    case class UserNotFoundException(name: String) extends Exception
    trait UserRepo {
      def findOne(name: String): Future[Option[User]]
    }
    val name      = "bob"
    val dummyUser = User("dummy")

    val userRepo = mock[UserRepo]
    when(userRepo.findOne(name)).thenReturn(Future.failed(new RuntimeException()))

    val userF = userRepo
      .findOne(name)
      .flatMap {
        case Some(user) ⇒ Future.successful(user)
        case None       ⇒ Future.failed(UserNotFoundException(name))
      }
      .recover {
        case NonFatal(_) ⇒ dummyUser
      }

    userF.futureValue shouldBe dummyUser
  }

• Update * After looking at the original post closely, I found small mistake in the way you are mocking. try below:

when(mockUserRepository.findOne(userKeys)).thenCallRealMethod()
when(mockUserRepository.getOneById(userKeys)).thenThrow(classOf[RuntimeException]) 

Notice thenCallRealMethod() here, earlier you were mocking findOne to return future with successful value which means original method was not getting called which in turn was not calling getOneById