tests.kt

class MainViewModelTest {

    @get:Rule
    val instantTaskRule = InstantTaskExecutorRule()

    @RelaxedMockK
    lateinit var mockObserver: Observer<Boolean>

    lateinit var viewModel: MainViewModel

    @Before
    fun setUp() {
        MockKAnnotations.init(this)

        viewModel = MainViewModel()
    }

    @Test
    fun testValidation() {
        viewModel.isFormValid.observeForever(mockObserver)

        viewModel.username = "username1"
        viewModel.password = "password1"
        viewModel.username = "username"

        verifyOrder {
            mockObserver.onChanged(false)
            mockObserver.onChanged(true)
            mockObserver.onChanged(false)
        }
    }
}