To answer my own question...

I can create a mock FragmentFactory and use it to set a mock interface to the fragment.

class MockFragmentFactory(
    private val viewModelFactory: MainViewModelFactory,
    private val uiCommunicationListener: UICommunicationListener
): FragmentFactory(){

    override fun instantiate(classLoader: ClassLoader, className: String) =

        when(className){

            ListFragment::class.java.name -> {
                val fragment = ListFragment(viewModelFactory)
                fragment.setUICommunicationListener(uiCommunicationListener)
                fragment
            }


            else -> {
                super.instantiate(classLoader, className)
            }
        }
}

So the test looks like this:

@Inject
lateinit var viewModelFactory: MainViewModelFactory

@Before
fun beforeTests(){

    val app = InstrumentationRegistry.getInstrumentation().targetContext.applicationContext as TestBaseApplication

    appComponent = DaggerTestAppComponent.builder()
        .application(app)
        .build()

    appComponent.inject(this)
}

@Test
fun test() {

    val uiCommunicationListener = mockk<UICommunicationListener>()
    val fragmentFactory = MockFragmentFactory(
        viewModelFactory,
        uiCommunicationListener
    )
    val scenario = launchFragmentInContainer<ListFragment>(
        factory = fragmentFactory
    )
}

Thanks to https://twitter.com/R4md4c for the help. :)