使用LiveData、协同程序和事务测试Android Room

Question

我想测试我的数据库层，我发现自己陷入了一种第22条军规的境地。

测试用例由两件事组成：

• 保存一些实体
• 加载实体并断言数据库映射按预期工作

简而言之，问题在于：

• Insert是一种suspend方法，这意味着它需要在runBlocking{}

我的道类是这样的：

@Dao
interface GameDao {
    @Query("SELECT * FROM game")
    fun getAll(): LiveData<List<Game>>

    @Insert
    suspend fun insert(game: Game): Long

    @Insert
    suspend fun insertRound(round: RoundRoom)

    @Transaction
    suspend fun insertGameAndRounds(game: Game, rounds: List<RoundRoom>) {
        val gameId = insert(game)
        rounds.onEach {
            it.gameId = gameId
        }

        rounds.forEach {
            insertRound(it)
        }
    }

测试用例是：

@RunWith(AndroidJUnit4::class)
class RoomTest {
    private lateinit var gameDao: GameDao
    private lateinit var db: AppDatabase

    @get:Rule
    val instantTaskExecutorRule = InstantTaskExecutorRule()

    @Before
    fun createDb() {
        val context = ApplicationProvider.getApplicationContext<Context>()
        db = Room.inMemoryDatabaseBuilder(
            context, AppDatabase::class.java
        ).build()
        gameDao = db.gameDao()
    }

    @Test
    @Throws(Exception::class)
    fun storeAndReadGame() {
        val game = Game(...)

        runBlocking {
            gameDao.insert(game)
        }

        val allGames = gameDao.getAll()

        // the .getValueBlocking cannot be run on the background thread - needs the InstantTaskExecutorRule
        val result = allGames.getValueBlocking() ?: throw InvalidObjectException("null returned as games")

        // some assertions about the result here
    }

    @Test
    fun storeAndReadGameLinkedWithRound() {
        val game = Game(...)

        val rounds = listOf(
            Round(...),
            Round(...),
            Round(...)
        )

        runBlocking {
            // This is where the execution freezes when InstantTaskExecutorRule is used
            gameDao.insertGameAndRounds(game, rounds)
        }

        // retrieve the data, assert on it, etc
    }
}

getValueBlocking是LiveData的一个扩展函数，基本上是从上面的链接复制粘贴的

fun <T> LiveData<T>.getValueBlocking(): T? {
    var value: T? = null
    val latch = CountDownLatch(1)

    val observer = Observer<T> { t ->
        value = t
        latch.countDown()
    }

    observeForever(observer)

    latch.await(2, TimeUnit.SECONDS)
    return value
}

测试这个场景的正确方法是什么？在开发数据库映射层时，我需要这些类型的测试，以确保一切都如我所期望的那样工作。

Answer 1

问题在于事务本身在内部某处使用运行阻塞，这会导致死锁。我已将InstantTaskExecutorRule更改为此类：

class IsMainExecutorRule : TestWatcher() {

    val defaultExecutor = DefaultTaskExecutor()

    override fun starting(description: Description?) {
        super.starting(description)
        ArchTaskExecutor.getInstance().setDelegate(object : TaskExecutor() {
            override fun executeOnDiskIO(runnable: Runnable) {
                defaultExecutor.executeOnDiskIO(runnable)
            }

            override fun postToMainThread(runnable: Runnable) {
                defaultExecutor.executeOnDiskIO(runnable)
            }

            override fun isMainThread(): Boolean {
                return true
            }
        })
    }

    override fun finished(description: Description?) {
        super.finished(description)
        ArchTaskExecutor.getInstance().setDelegate(null)
    }
}

然后在代码中它将是：

@get:Rule
val liveDataRule = IsMainExecutorRule()

它不会导致死锁，但仍允许观察实时数据。

Answer 2

这个问题现在有了一个解决方案，在这个答案中进行了解释。

修复方法是在内存数据库生成器中向文件室添加一行：

db = Room
    .inMemoryDatabaseBuilder(context, AppDatabase::class.java)
    .setTransactionExecutor(Executors.newSingleThreadExecutor()) // <-- this makes all the difference
    .build()

使用单线程执行器，测试工作正常。