Mocking generic interfaces with Kotlin and Mockito

Question

I am trying to mock a generic interface in Kotlin using Mockito. But so far I have found no natural solution. Given:

interface X<T> {
    fun x(): T
}

fun f(x: X<Int>) = x.x()

I could mock X with any of the following:

1. val x = f(Mockito.mock(X::class.java) as X<Int>)

   But that would generate an "unchecked cast" warning.

2. @Mock lateinit var x: X<Int>

   But I do not want to use the @Mock annotation because I like to have my fields final.

3. Introduce a helper function, as the mockito-kotlin library does:

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

   Then call it like this:

   val x: X<Int> = mock()

   But I do not want to use helper functions.

Is there an elegant pure Kotlin way to mock a generic interface with Mockito? (I would prefer a version of 1. without the warning.)

Answer 1

Just use mockito-kotlin project. This project contains all must have helpers for mockito. And supports mockito 2.1 as well.

Upd. To deal with "uncheked cast" use Reified type parameters.

You say that "But I do not want to use helper functions.", but why? This is inline function, so in compile time function will be inlined at all call sites will.