JUnit 5 Test - Unable to Observe Nested LiveData Value

Issue

Overview

Expected - Saving nested LiveData values in a local unit test, and then asserting their values.

Observed - Saving nested LiveData values in a ViewModel are observed successfully in production code, but fail in the local unit test. This is potentially due to the lack of threading in local unit tests vs. running on the Android environment.

Code

• ViewModel contains LOADING, CONTENT, and ERROR (LCE) conditions for when a user selects content to open.
• The LiveData NotifyItemChangedEffect state is saved in order to update the view.
• NotifyItemChangedEffect is saved inside of the function to save content sent to the view. Only in the CONTENT condition, the item selected is sent to the view with a LiveData object saved, ContentToPlay.
• In production, this works with the view's UI updating during LOADING, CONTENT, and ERROR, while ContentToPlay is only returned in the successful CONTENT condition.

ContentViewModel.kt

    is ContentSelected -> {
        _feedViewState.value = _feedViewState.value?.copy(

                // LiveData value for ContentToPlay initiated here.
                contentToPlay = switchMap(getAudiocast(contentSelected)) { lce ->
                    liveData {
                        when (lce) {
                            is Loading ->
                                _viewEffect.value = _viewEffect.value?.copy(
                                        notifyItemChanged = liveData {
                                            emit(Event(NotifyItemChangedEffect(...)))
                                        })
                            is Lce.Content -> {
                                _viewEffect.value = _viewEffect.value?.copy(
                                        notifyItemChanged = liveData {
                                            emit(Event(NotifyItemChangedEffect(...)))
                                        })

                                // LiveData value for ContentToPlay saved here.
                                emit(Event(lce.packet))
                            }
                            is Error -> {
                                _viewEffect.value = _viewEffect.value?.copy(
                                        notifyItemChanged = liveData {
                                            emit(Event(NotifyItemChangedEffect(...)))
                                        })
                                _viewEffect.value = _viewEffect.value?.copy(
                                        snackBar = liveData {
                                            emit(Event(SnackBarEffect(...)))
                                        })
                            }
                        }
                    }
                })
        ...
    }

• By design - ContentToPlay is not returned in the LOADING and ERROR conditions.
• Issue - The nested LiveData values for NotifyItemChangedEffect are not saved in the unit test, which update the view in each LCE condition. This code is executed inside of the LiveData saved for ContentToPlay. This pattern is logged and working in production.

PlayContentTests.kt

    @ExtendWith(InstantExecutorExtension::class)
    class PlayContentTests {
        @ParameterizedTest
        @MethodSource("FeedLoad")
        fun `Play Content`(test: PlayContentTest) = runBlocking {
            // ViewModel method included to initiate ContentSelected event.
            ...
            when (test.lceState) {
                LOADING ->
                    assertThat(contentViewModel.viewEffect.getOrAwaitValue().notifyItemChanged.getOrAwaitValue().peekEvent()).isEqualTo(
                            NotifyItemChangedEffect(...))
                CONTENT -> {
                    assertThat(contentViewModel.feedViewState.getOrAwaitValue().contentToPlay.getOrAwaitValue().peekEvent()).isEqualTo(
                            ContentToPlay(...))
                    assertThat(contentViewModel.viewEffect.getOrAwaitValue().notifyItemChanged.getOrAwaitValue().peekEvent()).isEqualTo(
                            NotifyItemChangedEffect(...))
                }
                ERROR -> {
                    assertThat(contentViewModel.feedViewState.getOrAwaitValue().contentToPlay.getOrAwaitValue().peekEvent()).isEqualTo(
                            ContentToPlay(...))
                    assertThat(contentViewModel.viewEffect.getOrAwaitValue().notifyItemChanged.getOrAwaitValue().peekEvent()).isEqualTo(
                            NotifyItemChangedEffect(...))
                }
            }
        }
    }

Solution

Saving LiveData in all (LCE) Loading, Content, Error conditions

Saving a ContentToPlay LiveData value or null in all LCE conditions of the ViewModel to ensure a value is returned synchronously for local unit testing.

Note - The downside of this strategy is it emits a ContentToPlay value unnecessarily to the view in production code which is not ideal, but does not appear to be a major issue.

ContentViewModel.kt

    _feedViewState.value = _feedViewState.value?.copy(contentToPlay =
    switchMap(getAudiocast(contentSelected)) { lce ->
        liveData {
            when (lce) {
                is Loading -> {
                    setContentLoadingStatus(contentSelected.content.id, View.VISIBLE)
                    _viewEffect.value = _viewEffect.value?.copy(
                            notifyItemChanged = liveData {
                                emit(Event(NotifyItemChangedEffect(contentSelected.position)))
                            })
                    // Empty ContentToPlay saved.
                    emit(Event(null))
                }
                is Lce.Content -> {
                    setContentLoadingStatus(contentSelected.content.id, View.GONE)
                    _viewEffect.value = _viewEffect.value?.copy(
                            notifyItemChanged = liveData {
                                emit(Event(NotifyItemChangedEffect(contentSelected.position)))
                            })
                    // ContentToPlay saved.
                    emit(Event(lce.packet))
                }
                is Error -> {
                    setContentLoadingStatus(contentSelected.content.id, View.GONE)
                    _viewEffect.value = _viewEffect.value?.copy(
                            notifyItemChanged = liveData {
                                emit(Event(NotifyItemChangedEffect(contentSelected.position)))
                            })
                    if (lce.packet.filePath.equals(TTS_CHAR_LIMIT_ERROR))
                        _viewEffect.value = _viewEffect.value?.copy(
                                snackBar = liveData {
                                    emit(Event(SnackBarEffect(TTS_CHAR_LIMIT_ERROR_MESSAGE)))
                                })
                    else _viewEffect.value = _viewEffect.value?.copy(
                            snackBar = liveData {
                                emit(Event(SnackBarEffect(CONTENT_PLAY_ERROR)))
                            })
                    // Empty ContentToPlay saved.
                    emit(Event(null))
                }
            }
        }
    })

Answered By - Adam Hurwitz