How to properly mock companion object methods?

[jselbo]

Consider a Kotlin class with companion object:

class MyClass {
    companion object {
        fun foo(): String {
            return "unmocked"
        }
    }
}

Intuitively, we might expect to use mockStatic(MyClass.Companion::class.java) and stub foo(). But this doesn't work as expected. (Note: if you mark with the method with @JvmStatic, you can stub the generated static wrapper method but only Java callsites will invoke this.)

We found a way to make stubbing companion object methods work by using mockConstruction:

mockConstruction(MyClass.Companion::class.java).use {
    whenever(MyClass.foo()).thenReturn("Mocked")

    val result = MyClass.foo()
    assertEquals("Mocked", result)
    verify(MyClass).foo()
}

This works because foo() as compiled is actually an instance method on the inner class MyClass$Companion. A callsite invoking the method is equivalent to:

val myClassCompanionInstance = MyClass.Companion
myClassCompanionInstance.foo()

where MyClass bytecode is equivalent to (expressed in Java):

class MyClass {
  static final Companion Companion;
  static {
    Companion = new Companion();
  }
  ....
}

Meanwhile, StackOverflow answers recommend refactoring the code to have a wrapper method, or use competing mocking frameworks like MockK or PowerMock:
https://stackoverflow.com/questions/53174839/unit-testing-verifying-a-companion-object-method-is-called-mocking-a-companion

Is using mockConstruction really the intended way to stub methods on Kotlin companion objects? If so, can you add this guidance to the wiki?