Mocking Extension functions

Is it possible to stub Kotlin extension methods?

Let’s say I have an extension function:

fun Context.findColor(color: Int) = resources.getColor(color)

And I have a mock of an Context I would like to stub:

val mock = mock<Context>()

whenever(mock.findColor(color)).thenReturn(color)

Right now it doesn’t work. Is there a way to achieve this?

[realdadfish]

If you have instance extension functions (which are basically syntactic sugar), you can easily use mockito-kotlin for them:

data class Bar(thing: Int)

class Foo {
   fun Bar.bla(anotherThing: Int): Int { ... }
}

val bar = Bar(thing = 1)
val foo = mock<Foo>()

with(foo) {
  whenever(any<Bar>().bla(any()).doReturn(3)
}

verify(foo).apply {
  bar.bla(anotherThing = 2)
}

[nhaarman]

I guess the ‘official’ answer would be “don’t mock extension functions”. They’re basically static functions, which Mockito does not support. Create a proper abstraction for them, or resort to tools like PowerMock or MocK.