MockK mock ViewModel's savedStateHandle.getLiveData()

Question

I'm trying to test this ViewModel with savedStateHandle

class PostListViewModel @ViewModelInject constructor(
    private val coroutineScope: CoroutineScope,
    private val getPostsUseCase: GetPostListUseCaseFlow,
    @Assisted savedStateHandle: SavedStateHandle
) : AbstractPostListVM() {

    private val _goToDetailScreen =
        savedStateHandle.getLiveData<Event<Post>>(POST_DETAIL)
//        MutableLiveData<Event<Post>>()

    override val goToDetailScreen: LiveData<Event<Post>>
        get() = _goToDetailScreen

    private val _postViewState =
        savedStateHandle.getLiveData<ViewState<List<Post>>>(POST_LIST)
//        MutableLiveData<ViewState<List<Post>>>()

    override val postViewState: LiveData<ViewState<List<Post>>>
        get() = _postViewState

    override fun getPosts() {

        getPostsUseCase.getPostFlowOfflineFirst()
            .convertToFlowViewState()
            .onStart {
                _postViewState.value = ViewState(status = Status.LOADING)
            }
            .onEach {
                _postViewState.value = it
            }
            .launchIn(coroutineScope)
    }

    override fun refreshPosts() {
        getPostsUseCase.getPostFlowOfflineLast()
            .convertToFlowViewState()
            .onStart {
                _postViewState.value = ViewState(status = Status.LOADING)
            }
            .onEach {
                _postViewState.value = it
            }
            .launchIn(coroutineScope)
    }

    override fun onClick(post: Post) {
        _goToDetailScreen.value = Event(post)
    }
}

And the test being

@Test
fun `given exception returned from useCase, should have ViewState ERROR offlineFirst`() =
    testCoroutineRule.runBlockingTest {

        // GIVEN
        every {
            savedStateHandle.getLiveData<ViewState<List<Post>>>(AbstractPostListVM.POST_LIST)
        } returns MutableLiveData()

        every {
            savedStateHandle.getLiveData<Event<Post>>(AbstractPostListVM.POST_DETAIL)
        } returns MutableLiveData()

        every {
            useCase.getPostFlowOfflineFirst()
        } returns flow<List<Post>> {
            emit(throw Exception("Network Exception"))
        }

        val testObserver = viewModel.postViewState.test()

        // WHEN
        viewModel.getPosts()

        // THEN
        testObserver
            .assertValue { states ->
                (states[0].status == Status.LOADING &&
                        states[1].status == Status.ERROR)
            }
            .dispose()

        val finalState = testObserver.values()[1]
        Truth.assertThat(finalState.error?.message).isEqualTo("Network Exception")
        Truth.assertThat(finalState.error).isInstanceOf(Exception::class.java)
        verify(atMost = 1) { useCase.getPostFlowOfflineFirst() }
    }

This test works when i use MutableLiveData instead of SavedStateHandle.getLiveData() with this and other tests.

With savedStateHandle being mocked as

private val savedStateHandle: SavedStateHandle = mockk()

returns

io.mockk.MockKException: no answer found for: SavedStateHandle(#2).getLiveData(POST_LIST)

and i changed mocked savedStateHandle to with relaxed = true

private val savedStateHandle: SavedStateHandle = mockk(relaxed = true)

based on this question.

Now value of postViewState does not change and test fails with

java.lang.IndexOutOfBoundsException: Index: 0, Size: 0

What is the correct way to mock and get LiveData with SavedStateHandle?

Hi @Thracian, have you find any solution?, I am also facing same issue. — Siddhpura Amit, Jan 26 '21 at 04:02
@PanchalAmit Sorry, but i haven't yet. I hope to get an answer. — Thracian, Jan 26 '21 at 06:47

score 10 · Accepted Answer · edited Feb 27 '23 at 16:51

I have find solution with MockK Library and it is working fine,

I have done by following way

val savedStateHandle = mockk<SavedStateHandle>(relaxed = true)

With above line I have created savedStateHandle which I have used in ViewModel

@Test
fun `test something simple`() {
    val savedStateHandle = mockk<SavedStateHandle>(relaxed = true)
    val viewModel = MyViewModel(savedStateHandle)
    verify { savedStateHandle.set(MyViewModel.KEY, "Something") }
}

You could also replace the set function with the indexing operator:

    verify { savedStateHandle[MyViewModel.KEY] = "Something" }

score 10 · Answer 2 · answered Jun 03 '21 at 20:08

Maybe it's because I use junit5, the selected answer didn't work for me.

In case it helps someone, what I did is to create a SavedStateHandle instance with the info I needed instead of mocking it in the first section of the test (in the Given/Arrange section) and initialising the ViewModel after that:

@Test
fun `whatever`() =
    coroutineRule.testDispatcher.runBlockingTest {
        val savedStateHandle = SavedStateHandle().apply {
            set(MyViewModel.KEY, "something")
        }
        val viewModel = PostListViewModel(coroutineScope, getPostsUseCase, savedStateHandle)

        ...
}

This is ideal No need to mock `SavedStateHandle`, you can just construct it and manipulate its data (and verify its state) directly on the instance itself. — Mitch Ware, Oct 05 '22 at 13:46

MockK mock ViewModel's savedStateHandle.getLiveData()

2 Answers2