Mockito with Scala does not mock "val" functions

I am using Mockito, ("org.mockito" % "mockito-core" % "1.8.5") in my Scala (version 2.11.11)-tests (Play Framework project)

Mocking a trait would always throw a JavaNullPointerException, the error was not helpful so I tried a several different things before someone suggested I try to change my val functions to def methods. (see my stack overflow question https://stackoverflow.com/q/44227298/4884034)

That solved it!

The error message should be more specific?

Here is my Repository trait:

trait UserRepository {
  val getConversations: (String) => Option[Vector[User]]
}

Here is my Service:

class UserService(userRepository: UserRepository){
  private val boolToNumber : (Boolean) => Int = (bool) => ... not useful here
  private val countToBool : (Int) => Boolean = (int) => ... not useful here

  val getParticipations: (String) => Option[Vector[User]] = (name) => {
    userRepository.getConversations(name) match {
    ... some implementation
  }
}

And my tests

  // init
  val userRepository = mock[UserRepository]

  // setup
  when(userRepository.getConversations("Smith")) thenReturn (
    Some(
      Vector(
        User("Smith", true, true, ConversationKey("Smith", "Smith and O'Connell chatroom")),
        User("Smith", false, true, ConversationKey("Smith", "Smith and O'Connell chatroom"))
      )
    )
  )
  val userService : UserService = new UserService(userRepository)
  // run
  val actual = userService.getParticipations("Smith")

  // verify
  actual mustBe Some(Vector(User("Smith", false, true, ConversationKey("Smith", "Smith and O'Connell chatroom"))))

[bbonanno]

@ThibaultUrien you are correct, if what you store in the val is a function (or any other object with behaviuor), and said object also needs to be mocked for whatever reason, then you need 2 mocks, one for MyTrait and, in this case, one for the function.

So you’d end up with something like

    val mt          = mock[MyTrait]
    val strProvider = mock[Int => String]
    mt.stringProvider returns strProvider

    strProvider(*) returns "bob"

    println(mt.stringProvider(3))

A shorter way to write this could be achieved using deep stubs

    val mt = mock[MyTrait](DefaultAnswers.ReturnsDeepStubs)
    mt.stringProvider(*) returns "bob"

    println(mt.stringProvider(3))

Those 2 snippets of code are semantically equivalent, the difference is that DeepStubs will create all the intermediate mocks for you, so you can save yourself some boilerplate, the downside of course is that you lose the SmartNulls behaviuor, so it’s up to you which flavour you prefer.

[bbonanno]

@djole103 I just tried this code

object MyClass extends App {

  import org.mockito.Mockito._

  trait MyTrait {
    val DefaultString = "myDefaultString"
    val DefaultInt = 42
  }

  val mt = mock(classOf[MyTrait])

  when(mt.DefaultString) thenReturn "Hi"
  when(mt.DefaultInt) thenReturn 7

  def printDefaults = {
    println(mt.DefaultString)
    println(mt.DefaultInt)
  }

  printDefaults
}

and it works as expected

this is what I put in my build.sbt

scalaVersion := "2.11.11"

libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.5" % Test
libraryDependencies += "org.mockito" % "mockito-core" % "1.9.5" % Test

Is there anything else that you’re doing that could be different from my setup?