要做到这一点,一个简单的方法就是模仿pagelist。这个乐趣将“转换”一个列表到一个页面列表(在这种情况下,我们不是使用真正的页面列表,而只是一个模拟版本,如果你需要实现页面列表的其他方法,在这个乐趣中添加它们)

 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
 }

1. 不能将列表强制转换为PagedList。
2. 不能仅通过数据源直接创建页面列表。一种方法是创建返回测试数据的fakedatasource。

如果是端到端的测试,可以只使用内存中的db。在调用之前添加测试数据。例子: https://medium.com/exploring-android/android-architecture-components-testing-your-room-dao-classes-e06e1c9a1535

使用mock datasource.factory将列表转换为PagedList

@saied89 分享了这个 solution 在这个 googlesamples/android-architecture-components 问题。我在 Coinverse Open App 为了使用kotlin、junit 5、mockk和assertj库对viewmodel进行本地单元测试。

从我使用过的页面列表中观察实时数据 Jose Alcérreca's implementation 属于 getOrAwaitValue 从 LiveDataSample sample app 在google的android架构组件示例下。

这个 asPagedList 在示例测试中实现了扩展函数 contentViewModelTest.kt 下面。

pagedListTestUtil.kt页

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(config: PagedList.Config? = null): PagedList<T>? {
    val defaultConfig = PagedList.Config.Builder()
        .setEnablePlaceholders(false)
        .setPageSize(size)
        .setMaxSize(size + 2)
        .setPrefetchDistance(1)
        .build()
    return LivePagedListBuilder<Int, T>(
        createMockDataSourceFactory(this),
        config ?: defaultConfig
    ).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
}

contentViewModelTest.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 MutableLiveData<Lce<ContentResult.PagedListResult>>().also { lce ->
            lce.value = Lce.Content(
                ContentResult.PagedListResult(
                    pagedList = MutableLiveData<PagedList<Content>>().apply {
                        this.value = listOf(content).asPagedList(
                            PagedList.Config.Builder().setEnablePlaceholders(false)
                                .setPrefetchDistance(24)
                                .setPageSize(12)
                                .build())
                        }, 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,以确保观察器不在主线程上。下面是 Jeroen Mols' implementation 是的。

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)
    }
}