ViewModel unit test - Using delays

I am new to testing and I am writing a test for my ViewModel. I have a couple of questions about it.

1. In my Test method, unless I add a delay(10), the test fails saying:

Wanted but not invoked: breweryRepository.getBeerStyles(); -> at com.helenc.test.repositories.BreweryRepository.getBeerStyles(BreweryRepository.kt:12) Actually, there were zero interactions with this mock.

Why do I need a delay? Is there a better way to do it?

2. I added the test in the test folder (not in androidTest). Is this correct? I am not sure since I am using some androidx dependencies, like androidx.lifecycle.Observer or androidx.arch.core.executor.testing.InstantTaskExecutorRule.

This is my ViewModel test file:

@RunWith(JUnit4::class)
class BeerStylesViewModelTest {

    private lateinit var viewModel: BeerStylesViewModel
    private lateinit var repository: BreweryRepository
    private lateinit var beerStylesObserver: Observer<Resource<List<StylesData>>>

    private val successResource = Resource.success(mockedBeerStylesList)

    @Rule
    @JvmField
    val instantExecutorRule = InstantTaskExecutorRule()

    @ObsoleteCoroutinesApi
    private val mainThreadSurrogate = newSingleThreadContext("UI thread")

    @ObsoleteCoroutinesApi
    @ExperimentalCoroutinesApi
    @Before
    fun setUp() {
        Dispatchers.setMain(mainThreadSurrogate)
        repository = mock()
        runBlocking {
            whenever(repository.getBeerStyles()).thenReturn(successResource)
        }
        viewModel = BeerStylesViewModel(repository)
        beerStylesObserver = mock()
    }

    @Test
    fun `when load beerStyles success`() = runBlocking {
        viewModel.beerStyles.observeForever(beerStylesObserver)
        delay(10)
        verify(repository).getBeerStyles()
        verify(beerStylesObserver).onChanged(Resource.loading(null))
        verify(beerStylesObserver).onChanged(successResource)
    }

    @ObsoleteCoroutinesApi
    @ExperimentalCoroutinesApi
    @After
    fun tearDown() {
        Dispatchers.resetMain()
        mainThreadSurrogate.close()
    }
}