CODEWITHSUNDEEP
androidunit-testingmockitoandroid-viewmodelrx-kotlin
Ackbryy
Ackbryy

Reputation: 41

Unit Test : Observer onChanged should be called twice instead of once

Why do I get different results when unit testing my ViewModel?

I got two tests. When I launch each test individually that's ok but when I launch all tests in a row I got an error. It's a ViewModel that change state each time I got a return from an API. I expect to get android.arch.lifecycle.Observer.onChanged called two times but it's just called once for the second test. Unit test works fine when I replace verify(view, times(2)).onChanged(arg.capture()) with verify(view, atLeastOnce()).onChanged(arg.capture()) at the first test.

UserViewModel :

class UserViewModel(
        private val leApi: LeApi
): ViewModel() {
    private val _states = MutableLiveData<ViewModelState>()
    val states: LiveData<ViewModelState>
        get() = _states

    fun getCurrentUser() {
        _states.value = LoadingState
        leApi.getCurrentUser()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(
                        { user -> _states.value = UserConnected(user) },
                        { t -> _states.value = FailedState(t) }
                )
        }
    }
}

UserViewModelTest :

@RunWith(MockitoJUnitRunner::class)
class UserViewModelTest {

    lateinit var userViewModel: UserViewModel

    @Mock
    lateinit var view: Observer<ViewModelState>

    @Mock
    lateinit var leApi: LeApi

    @get:Rule
    val rule = InstantTaskExecutorRule()

    @Before
    fun setUp() {
        RxAndroidPlugins.setInitMainThreadSchedulerHandler { Schedulers.trampoline() }
        userViewModel = UserViewModel(leApi)
        userViewModel.states.observeForever(view)
    }

    @Test
    fun testGetCurrentUser() {
        val user = Mockito.mock(User::class.java)
        `when`(leApi.getCurrentUser()).thenReturn(Single.just(user))
        userViewModel.getCurrentUser()

        val arg = ArgumentCaptor.forClass(ViewModelState::class.java)
        verify(view, times(2)).onChanged(arg.capture())

        val values = arg.allValues

        assertEquals(2, values.size)
        assertEquals(LoadingState, values[0])
        assertEquals(UserConnected(user), values[1])
    }

    @Test
    fun testGetCurrentUserFailed() {
        val error = Throwable("Got error")
        `when`(leApi.getCurrentUser()).thenReturn(Single.error(error))
        userViewModel.getCurrentUser()

        val arg = ArgumentCaptor.forClass(ViewModelState::class.java)
        verify(view, times(2)).onChanged(arg.capture()) // Error occurred here. That's the 70th line from stack trace.

        val values = arg.allValues
        assertEquals(2, values.size)
        assertEquals(LoadingState, values[0])
        assertEquals(FailedState(error), values[1])
    }
}

Expected : All tests passed.

Actual :

org.mockito.exceptions.verification.TooLittleActualInvocations: 
view.onChanged(<Capturing argument>);
Wanted 2 times:
-> at com.dev.titi.toto.mvvm.UserViewModelTest.testGetCurrentUserFailed(UserViewModelTest.kt:70)
But was 1 time:
-> at android.arch.lifecycle.LiveData.considerNotify(LiveData.java:109)

Upvotes: 4

Views: 4892

Answers (1)

solidogen
solidogen

Reputation: 649

I had this exact problem. I changed the way of testing to following (Google recommendations, here are the classes used for following test):

Add coroutines to your project, since test helpers use them:

implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.2.0")
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.1.1")
testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.3.0'

Get rid of this line:

lateinit var view: Observer<ViewModelState>

Then change your test to following:

private val testDispatcher = TestCoroutineDispatcher()

@Before
fun setup() {
    Dispatchers.setMain(testDispatcher)
    ...
}

@After
fun tearDown() {
    Dispatchers.resetMain()
    testDispatcher.cleanupTestCoroutines()
    ...
}

@Test
fun testGetCurrentUser() {
    runBlocking {
        val user = Mockito.mock(User::class.java)
        `when`(leApi.getCurrentUser()).thenReturn(Single.just(user))
        userViewModel.states.captureValues {
            userViewModel.getCurrentUser()
            assertSendsValues(100, LoadingState, UserConnected(user))
        }
    }
}

Upvotes: 2

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