如何为测试创建对象的PagedList？

Question

我一直在与谷歌的拱库一起工作,但是让测试变得困难的一件事就是合作PagedList.

对于此示例,我使用存储库模式并从API或网络返回详细信息.

所以在ViewModel中我调用了这个接口方法:

override fun getFoos(): Observable<PagedList<Foo>>

然后,存储库将RxPagedListBuilder用于创建Observable类型为PagedList的类型:

 override fun getFoos(): Observable<PagedList<Foo>> =
            RxPagedListBuilder(database.fooDao().selectAll(), PAGED_LIST_CONFIG).buildObservable()

我希望能够通过这些返回a的方法设置返回测试PagedList<Foo>.类似的东西

when(repository.getFoos()).thenReturn(Observable.just(TEST_PAGED_LIST_OF_FOOS)

两个问题:

1. 这可能吗？
2. 我该如何创建PagedList<Foo>？

我的目标是以更加端到端的方式进行验证(例如确保在屏幕上显示正确的Foos列表).片段/活动/视图是PagedList<Foo>从ViewModel 观察的片段/活动/视图.

Answer 1

分页 3

Paging 3 库提供了一个构建器方法PagingData.from(someList)。

分页 2

使用 Mock 将 List 转换为 PagedList DataSource.Factory。

@saied89在这个googlesamples/android-architecture-components问题中分享了这个解决方案。我已经在Coinverse Open App中实现了模拟的PagedList，以便使用 Kotlin、JUnit 5、MockK 和 AssertJ 库对 ViewModel 进行本地单元测试。

观察从PagedList我用LiveData何塞Alcérreca的 实施的getOrAwaitValue从LiveDataSample示例应用程序在谷歌的Android体系结构组件样品。

该asPagedList扩展功能在样品测试实施ContentViewModelTest.kt下方。

PagedListTestUtil.kt

    import android.database.Cursor
    import androidx.paging.DataSource
    import androidx.paging.LivePagedListBuilder
    import androidx.paging.PagedList
    import androidx.room.RoomDatabase
    import androidx.room.RoomSQLiteQuery
    import androidx.room.paging.LimitOffsetDataSource
    import io.mockk.every
    import io.mockk.mockk

    fun <T> List<T>.asPagedList() = LivePagedListBuilder<Int, T>(createMockDataSourceFactory(this),
        Config(enablePlaceholders = false,
                prefetchDistance = 24,
                pageSize = if (size == 0) 1 else size))
        .build().getOrAwaitValue()

    private fun <T> createMockDataSourceFactory(itemList: List<T>): DataSource.Factory<Int, T> =
        object : DataSource.Factory<Int, T>() {
            override fun create(): DataSource<Int, T> = MockLimitDataSource(itemList)
        }

    private val mockQuery = mockk<RoomSQLiteQuery> {
        every { sql } returns ""
    }

    private val mockDb = mockk<RoomDatabase> {
        every { invalidationTracker } returns mockk(relaxUnitFun = true)
    }

    class MockLimitDataSource<T>(private val itemList: List<T>) : LimitOffsetDataSource<T>(mockDb, mockQuery, false, null) {
        override fun convertRows(cursor: Cursor?): MutableList<T> = itemList.toMutableList()
        override fun countItems(): Int = itemList.count()
        override fun isInvalid(): Boolean = false
        override fun loadRange(params: LoadRangeParams, callback: LoadRangeCallback<T>) { /* Not implemented */ }

        override fun loadRange(startPosition: Int, loadCount: Int) =
            itemList.subList(startPosition, startPosition + loadCount).toMutableList()

        override fun loadInitial(params: LoadInitialParams, callback: LoadInitialCallback<T>) {
            callback.onResult(itemList, 0)
        }
    }

LiveDataTestUtil.kt

    import androidx.lifecycle.LiveData
    import androidx.lifecycle.Observer
    import java.util.concurrent.CountDownLatch
    import java.util.concurrent.TimeUnit
    import java.util.concurrent.TimeoutException

    /**
     * Gets the value of a [LiveData] or waits for it to have one, with a timeout.
     *
     * Use this extension from host-side (JVM) tests. It's recommended to use it alongside
     * `InstantTaskExecutorRule` or a similar mechanism to execute tasks synchronously.
     */
    fun <T> LiveData<T>.getOrAwaitValue(
        time: Long = 2,
        timeUnit: TimeUnit = TimeUnit.SECONDS,
        afterObserve: () -> Unit = {}
    ): T {
        var data: T? = null
        val latch = CountDownLatch(1)
        val observer = object : Observer<T> {
            override fun onChanged(o: T?) {
                data = o
                latch.countDown()
                this@getOrAwaitValue.removeObserver(this)
            }
        }
        this.observeForever(observer)
        afterObserve.invoke()
        // Don't wait indefinitely if the LiveData is not set.
        if (!latch.await(time, timeUnit)) {
            this.removeObserver(observer)
            throw TimeoutException("LiveData value was never set.")
        }
        @Suppress("UNCHECKED_CAST")
        return data as T
    }

内容视图模型测试.kt

    ...
    import androidx.paging.PagedList
    import com.google.firebase.Timestamp
    import io.mockk.*
    import org.assertj.core.api.Assertions.assertThat
    import org.junit.jupiter.api.AfterAll
    import org.junit.jupiter.api.BeforeAll
    import org.junit.jupiter.api.BeforeEach
    import org.junit.jupiter.api.Test
    import org.junit.jupiter.api.extension.ExtendWith

    @ExtendWith(InstantExecutorExtension::class)
    class ContentViewModelTest {
        val timestamp = getTimeframe(DAY)

        @BeforeAll
        fun beforeAll() {
            mockkObject(ContentRepository)
        }

        @BeforeEach
        fun beforeEach() {
            clearAllMocks()
        }

        @AfterAll
        fun afterAll() {
            unmockkAll()
        }

        @Test
        fun `Feed Load`() {
            val content = Content("85", 0.0, Enums.ContentType.NONE, Timestamp.now(), "",
                "", "", "", "", "", "", MAIN,
                0, 0.0, 0.0, 0.0, 0.0,
                0.0, 0.0, 0.0, 0.0)
            every {
                getMainFeedList(any(), any())
            } returns liveData { 
               emit(Lce.Content(
                   ContentResult.PagedListResult(
                        pagedList = liveData {emit(listOf(content).asPagedList())}, 
                        errorMessage = ""))
            }
            val contentViewModel = ContentViewModel(ContentRepository)
            contentViewModel.processEvent(ContentViewEvent.FeedLoad(MAIN, DAY, timestamp, false))
            assertThat(contentViewModel.feedViewState.getOrAwaitValue().contentList.getOrAwaitValue()[0])
                .isEqualTo(content)
            assertThat(contentViewModel.feedViewState.getOrAwaitValue().toolbar).isEqualTo(
                ToolbarState(
                        visibility = GONE,
                        titleRes = app_name,
                        isSupportActionBarEnabled = false))
            verify {
                getMainFeedList(any(), any())
            }
            confirmVerified(ContentRepository)
        }
    }

InstantExecutorExtension.kt

使用 LiveData 时，JUnit 5 需要这样做，以确保观察者不在主线程上。下面是Jeroen Mols 的 实现。

    import androidx.arch.core.executor.ArchTaskExecutor
    import androidx.arch.core.executor.TaskExecutor
    import org.junit.jupiter.api.extension.AfterEachCallback
    import org.junit.jupiter.api.extension.BeforeEachCallback
    import org.junit.jupiter.api.extension.ExtensionContext

    class InstantExecutorExtension : BeforeEachCallback, AfterEachCallback {
        override fun beforeEach(context: ExtensionContext?) {
            ArchTaskExecutor.getInstance().setDelegate(object : TaskExecutor() {
                override fun executeOnDiskIO(runnable: Runnable) = runnable.run()
                override fun postToMainThread(runnable: Runnable) = runnable.run()
                override fun isMainThread(): Boolean = true
            })
        }

        override fun afterEach(context: ExtensionContext?) {
            ArchTaskExecutor.getInstance().setDelegate(null)
        }
    }

Answer 2

实现此目的的一种简单方法是模拟PagedList。这个有趣的操作会将列表“转换”为PagedList（在这种情况下，我们使用的不是真正的PagedList，而是模拟版本，如果您需要实现PagedList的其他方法，请在此方法中添加它们）

 fun <T> mockPagedList(list: List<T>): PagedList<T> {
     val pagedList = Mockito.mock(PagedList::class.java) as PagedList<T>
     Mockito.`when`(pagedList.get(ArgumentMatchers.anyInt())).then { invocation ->
        val index = invocation.arguments.first() as Int
        list[index]
     }
     Mockito.`when`(pagedList.size).thenReturn(list.size)
     return pagedList
 }

Answer 3

1. 您不能将 List 转换为 PagedList。
2. 不能直接创建PagedList，只能通过DataSource创建。一种方法是创建返回测试数据的 FakeDataSource。

如果是端到端测试，您可以只使用内存数据库。在调用之前添加您的测试数据。示例： https: //medium.com/exploring-android/android-architecture-components-testing-your-room-dao-classes-e06e1c9a15 ​​35