Mockito when clause not working in kotlin

Question

I am trying to use mockito in kotlin. I created the following test:

class HeroesDataSourceTest {

    @Mock
    lateinit var heroesRepository: HeroesRepository
    @Mock
    lateinit var params: PageKeyedDataSource.LoadInitialParams<Int>
    @Mock
    lateinit var callback: PageKeyedDataSource.LoadInitialCallback<Int, Heroes.Hero>

    val hero = Heroes.Hero(1, "superman", "holasuperman", 1, null, null)
    val results = Arrays.asList(hero)
    val data = Heroes.Data(results)
    val dataResult = Heroes.DataResult(data)

    val compositeDisposable = CompositeDisposable()

    lateinit var heroesDataSource: HeroesDataSource
    private val heroesPublishSubject = PublishSubject.create<Heroes.DataResult>()

    @Before
    fun initTest(){
        MockitoAnnotations.initMocks(this)

    }

    @Test
    fun testLoadInitialSuccess(){
        `when`(heroesRepository.getHeroes(ArgumentMatchers.anyInt())).thenReturn(heroesPublishSubject.singleOrError())
        heroesDataSource = HeroesDataSource(heroesRepository, compositeDisposable)
        val testObserver = TestObserver<Heroes.DataResult>()
        heroesDataSource.loadInitial(params, callback)
        heroesPublishSubject.onNext(dataResult)
        testObserver.assertComplete()
    }

}

But when I execute it in the line when(heroesRepository.getHeroes(ArgumentMatchers.anyInt())).thenReturn(heroesPublishSubject.singleOrError()) it just enter to getHeroes method instead of mocking it (and for sure since heroesRepository is not initialized because is mocket the method fails). I use this tons of times in java and it never gave me a single problem. What I have to do in kotlin to mock it properly?

EDIT

Here I put also HeroesRepository class

open class HeroesRepository {

    val privateKey = "5009bb73066f50f127907511e70f691cd3f2bb2c"
    val publicKey = "51ef4d355f513641b490a80d32503852"
    val apiDataSource = DataModule.create()
    val pageSize = 20

    fun getHeroes(page: Int): Single<Heroes.DataResult> {
        val now = Date().time.toString()
        val hash = generateHash(now + privateKey + publicKey)
        val offset: Int = page * pageSize
        return apiDataSource.getHeroes(now, publicKey, hash, offset, pageSize)
    }

    fun generateHash(variable: String): String {
        val md = MessageDigest.getInstance("MD5")
        val digested = md.digest(variable.toByteArray())
        return digested.joinToString("") {
            String.format("%02x", it)
        }
    }
}

Answer 1

Without adding another dependency, you can replace using the @Mock annotation with a helper function somewhere:

inline fun <reified T> mock(): T =
        Mockito.mock(T::class.java)

// To avoid having to use backticks for "when"
fun <T> whenever(methodCall: T): OngoingStubbing<T> =
        Mockito.`when`(methodCall)

Then in your test:

val heroesRepository: HeroesRepository = mock()

@Test
fun yourTest() {
    whenever(heroesRepository.getHeroes(ArgumentMatchers.anyInt()))
        .thenReturn(heroesPublishSubject.singleOrError())
}

Like you had before. This should work, because you're not expecting Mockito to deal with @Mock lateinit var, which it seems to be struggling with, and instead instantiating the mock yourself.