Mock ViewModel on Fragment UI Test

[nuxzero]

From GithubBrowserSample project. I got problem when I mock ViewModel to use to test Fragment but it look like mock not working. It still call Repository in ViewModel.

Here is code in test class

   @Before
    fun setUp() {
        viewModel = mock(AViewModel::class.java)
        `when`(viewModel.results).thenReturn(results)
        fragment = AFragment()
        fragment.viewModelFactory = ViewModelUtil.createFor(viewModel)
        activityRule.activity.setFragment(fragment)
    }

Inside fragment

open class AFragment : Fragment() {
    @Inject lateinit var viewModelFactory: ViewModelProvider.Factory
    private lateinit var viewModel: AViewModel
    lateinit var binding: AFragmentBinding

    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        binding = DataBindingUtil.inflate(inflater, R.layout.a_fragment, container, false)
        return binding.root
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        viewModel = ViewModelProviders.of(this, viewModelFactory).get(AViewModel::class.java)
        ...
    }
...

Do I need to use the FragmentDataBindingComponent from the sample?

[nuxzero]

My solution for this problem. I hope this will help some people that got problem about mock ViewModel for test fragment.

AFragmentTest.kt

@RunWith(AndroidJUnit4::class)
class AFragmentTest {

    @Rule
    @JvmField
    val activityRule = ActivityTestRule(TestSingleFragmentActivity::class.java, true, true)

    @Rule
    @JvmField
    val taskRule = TaskExecutorWithIdlingResourceRule()

    private lateinit var fragment: AFragment
    private lateinit var viewModel: AViewModel
    private val aData = MutableLiveData<Resource<A>>()
    private lateinit var fragmentBindingAdapters: FragmentBindingAdapters
    private lateinit var fragmentDataBindingComponent: FragmentDataBindingComponent

    @Before
    fun setUp() {
        fragment = AFragment()
        viewModel = mock(AViewModel::class.java)
        fragment.viewModel = viewModel

        // Mock DataBindingComponent and set to fragment
        fragmentBindingAdapters = mock(FragmentBindingAdapters::class.java)
        fragmentDataBindingComponent = mock(FragmentDataBindingComponent::class.java)
        `when`(fragmentDataBindingComponent.fragmentBindingAdapters).thenReturn(fragmentBindingAdapters)
        fragment.dataBindingComponent = fragmentDataBindingComponent

        `when`(viewModel.aData).thenReturn(aData)

        activityRule.activity.setFragment(fragment)
    }
...

AFragment.kt

class AFragment : Fragment() {

    @Inject lateinit var viewModelFactory: ViewModelProvider.Factory
    var viewModel: AViewModel? = null
    lateinit var binding: AFragmentBinding

    // DataBindingComponent required for UI test
    var dataBindingComponent: DataBindingComponent = FragmentDataBindingComponent(this)

    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Also need to set dataBindingComponent to binding object.
        binding = DataBindingUtil.inflate(inflater, R.layout.a_fragment, container, false, dataBindingComponent)
        return binding.root
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)

        // This protected fragment create new viewModel after create mock. 
        // If mock already created, no need to set viewModel.
        if(viewModel  == null) {
            viewModel = ViewModelProviders.of(this, viewModelFactory).get(AViewModel::class.java)
        }

    }
...

[JoaquimLey]

This works ofc, but this is not the proper solution I would say, you are exposing your ViewModel, it should be private, and if possible not set after fragment instantiation.

[SrishtiRoy]

i am using roboelectric for the same ,but still could not mock viewmodel

[JoaquimLey]

@SrishtiRoy have you tried mocking the ViewModel factory and return your own viewmodel instance?

Joaquim Ley

🌎: joaquimley.com http://www.joaquimley.com/ 📍Copenhagen, Denmark [image: Twitter Joaquim Ley] https://twitter.com/joaquimley https://github.com/joaquimley https://twitch.tv/joaquimley https://medium.com/@JoaquimLey

On Wed, Jan 30, 2019 at 5:04 AM SrishtiRoy notifications@github.com wrote:

i am using roboelectric for the same ,but still could not mock viewmodel

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/googlesamples/android-architecture-components/issues/196#issuecomment-458804027, or mute the thread https://github.com/notifications/unsubscribe-auth/AGmh_LuvvDitPpQ3dSO8FIXUY6L2WUPnks5vIRm-gaJpZM4PyBd5 .

[SrishtiRoy]

@JoaquimLey that worked ,just want to know does Data Binding in xml does not work with roboelectric, i am not able to access value that are set in viewmodel as observable field [@Test public void clickLogInButton_CallsViewModel() { Assert.assertNotNull(fragment);

    Button fav = fragment.getView().findViewById(R.id.fav);
    assertTrue(fav.getVisibility() == View.VISIBLE);
    assertEquals(fav.getText(),"Unfavorite");

    fav.performClick();

   verify(mockViewModel).setFavorite();
}](url)

[JoaquimLey]

Sorry, can't help you with that, never used robolectric with databinding :\

[vejei]

The reason the mock object does not work is because it was replaced when the dependency was injected，here is my solution to mock the ViewModel, in your test class add:

val viewModel = mock(MyViewModel::class.java)

fragmentManager.registerFragmentLifecycleCallbacks(object : FragmentManager.FragmentLifecycleCallbacks() {
    /*
    In general, dependencies are injected in the onAttach method.
    So, we can replace the injected ViewModel with a mock ViewModel after the method called.
    The method execution order in fragment: onAttach -> onCreate -> onCreateView -> onFragmentViewCreated
    */
    override fun onFragmentViewCreated(
        fm: FragmentManager,
        f: Fragment,
        v: View,
        savedInstanceState: Bundle?
    ) {
        (f as SignInFragment).viewModel = viewModel // replace ViewModel with the mock one
    }
}, false)