Transformed LiveData's value is always null in unit testing even when observed, but works fine in the UI

I want to test a LiveData's value. This LiveData's value depends on another LiveData in the ViewModel. When I run the app, the UI is working as intended. However, when I create a unit test to test the dependent LiveData, the test always fails with an AssertionError saying that the value is always null.

I have the following LiveData in my ViewModel.

class MovieViewModel @ViewModelInject constructor(
    private val movieRepository: MovieRepository
) : ViewModel() {
    private val state = movieRepository.getMoviesState()
    val errorLoading: LiveData<Boolean>
        get() = Transformations.map(state) { it == State.ERROR }
    val isLoading: LiveData<Boolean>
        get() = Transformations.map(state) { it == State.LOADING }
    ...
}

The LiveData I want to test are errorLoading and isLoading. To do that, I use Mockk to mock objects and have the following code to test them both.

    @Test
    fun ensure_isLoading_is_true_when_state_is_loading() {
        ...
        every { movieRepository.getMoviesState() } returns MutableLiveData(State.LOADING)
        every { booleanObserver.onChanged(any()) } just runs
        viewmodel = MovieViewModel(movieRepository)
        verify { movieRepository.getMoviesState() }
        viewmodel.isLoading.observeForever(booleanObserver)
        verify { booleanObserver.onChanged(true) }
        assertEquals(true, viewmodel.isLoading.value)
        viewmodel.isLoading.removeObserver(booleanObserver)
    }

So far, the test can verify that onChanged on the mocked Observer is called and the value of the new change is also correct. However, when I want to access the value of the LiveData I want to test, it always returns null.

I am aware that the LiveData needs to be observed and I have made a mock Observer to do that. However, the test still fails. Why does it always return null?

from Transformed LiveData's value is always null in unit testing even when observed, but works fine in the UI