Mocking extension function in Kotlin

Question

How to mock Kotlin extension function using Mockito or PowerMock in tests? Since they are resolved statically should they be tested as static method calls or as non static?

Answer 1

Instance extension functions can be stubbed and verified like this with the help of mockito-kotlin:

data class Bar(thing: Int)

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

val bar = Bar(thing = 1)
val foo = mock()

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

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