TechQA.

Jetpack Datastore: how can I test that my IOException handling is working correctly?

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WE have a solution in which we have a few data points that are stored in a Perferences Datastore. We realised that we had failed to account for the IOException correctly, and made a fix.

For peace of mind, I want to write a quick implementation test to just confirm that I have correctly handled it when we get an IOException from the data store. Something is wrong with how I'm writing my test, so that the IOException is not getting captured.

What am I missing about how I need to test this? Is it because I have a mock flow instead of a real one?

The current code is below, my expectation is that the IOException is properly handled during flow processing, but it currently still throws the IOException rather than returning NOT_FOUND

code under test:

class HubConfigurationLocalDataSource @Inject constructor(private val configurationsDataStore: DataStore<Preferences>) {

    private val logger = LoggerFactory.getLogger(this::class.java)

    private object HubConfigurationKeys {
        val CONFIGURATION_LAST_UPDATED = longPreferencesKey("configuration_last_updated")
        val CONFIGURATION_STATUS = stringPreferencesKey("configuration_status")
    }

    val configurationStatus: Flow<HubConfigurationStatusOnRemote> =
        configurationsDataStore.data.catch { exception ->
            when (exception) {
                is IOException -> logger.error(
                    "IOException encountered when retrieving hub configurations.",
                    exception
                )

                else -> logger.error(
                    "retrieval from datastore failed for unknown reason",
                    exception
                )
            }
            emit(emptyPreferences())
        }.map { preferences ->
            val stringFromPreferences = preferences[HubConfigurationKeys.CONFIGURATION_STATUS]
            stringFromPreferences?.let {
                HubConfigurationStatusOnRemote.valueOf(it.uppercase())
            } ?: HubConfigurationStatusOnRemote.NOT_FOUND
        }
}

Here is the test:


@ExtendWith(MockKExtension::class)
class HubConfigurationLocalDataSourceTest {

    @MockK
    lateinit var mockDataStore: DataStore<Preferences>

    lateinit var sut: HubConfigurationLocalDataSource

    @Test
    fun `If the data store throws an IOException, it is suppressed and Unknown is returned`() = runTest {
        //given
        coEvery { mockDataStore.data} throws IOException()
        sut = HubConfigurationLocalDataSource(mockDataStore)
        //expect
        assertEquals(HubConfigurationStatusOnRemote.NOT_FOUND, sut.configurationStatus.first())
    }
}

Here's what we got:

12:46:20.133 [Test worker @kotlinx.coroutines.test runner#2] DEBUG io.mockk.impl.instantiation.AbstractMockFactory - Creating mockk for Flow name=child of mockDataStore#1#2
12:46:20.146 [Test worker @kotlinx.coroutines.test runner#2] DEBUG io.mockk.impl.recording.states.AnsweringState - Throwing java.io.IOException on DataStore(mockDataStore#1).getData()

java.io.IOException
    at com.medixine.devicehub.repository.configuration.datasource.HubConfigurationLocalDataSourceTest$If the data store throws an IOException, it is suppressed and Unknown is returned$1.invokeSuspend(HubConfigurationLocalDataSourceTest.kt:27)
    at com.medixine.devicehub.repository.configuration.datasource.HubConfigurationLocalDataSourceTest$If the data store throws an IOException, it is suppressed and Unknown is returned$1.invoke(HubConfigurationLocalDataSourceTest.kt)
    at com.medixine.devicehub.repository.configuration.datasource.HubConfigurationLocalDataSourceTest$If the data store throws an IOException, it is suppressed and Unknown is returned$1.invoke(HubConfigurationLocalDataSourceTest.kt)
    at kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt$runTest$2$1$1.invokeSuspend(TestBuilders.kt:314)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at kotlinx.coroutines.test.TestDispatcher.processEvent$kotlinx_coroutines_test(TestDispatcher.kt:28)
    at kotlinx.coroutines.test.TestCoroutineScheduler.tryRunNextTaskUnless$kotlinx_coroutines_test(TestCoroutineScheduler.kt:103)
    at kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt$runTest$2$1$workRunner$1.invokeSuspend(TestBuilders.kt:320)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:280)
    at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:85)
    at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:59)
    at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)
    at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:38)
    at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)
    at kotlinx.coroutines.test.TestBuildersJvmKt.createTestResult(TestBuildersJvm.kt:13)
    at kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt.runTest-8Mi8wO0(TestBuilders.kt:308)
    at kotlinx.coroutines.test.TestBuildersKt.runTest-8Mi8wO0(Unknown Source)
    at kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt.runTest-8Mi8wO0(TestBuilders.kt:166)
    at kotlinx.coroutines.test.TestBuildersKt.runTest-8Mi8wO0(Unknown Source)
    at kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt.runTest-8Mi8wO0$default(TestBuilders.kt:158)
    at kotlinx.coroutines.test.TestBuildersKt.runTest-8Mi8wO0$default(Unknown Source)
    at com.medixine.devicehub.repository.configuration.datasource.HubConfigurationLocalDataSourceTest.If the data store throws an IOException, it is suppressed and Unknown is returned(HubConfigurationLocalDataSourceTest.kt:25)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.base/java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:727)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
    at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:156)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:147)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:86)
    at org.junit.jupiter.engine.execution.InterceptingExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(InterceptingExecutableInvoker.java:103)
    at org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.lambda$invoke$0(InterceptingExecutableInvoker.java:93)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
    at org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:92)
    at org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:86)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$7(TestMethodTestDescriptor.java:217)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:213)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:138)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:68)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:151)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at java.base/java.util.ArrayList.forEach(Unknown Source)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at java.base/java.util.ArrayList.forEach(Unknown Source)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:107)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:114)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:86)
    at org.junit.platform.launcher.core.DefaultLauncherSession$DelegatingLauncher.execute(DefaultLauncherSession.java:86)
    at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.processAllTestClasses(JUnitPlatformTestClassProcessor.java:110)
    at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.access$000(JUnitPlatformTestClassProcessor.java:90)
    at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.stop(JUnitPlatformTestClassProcessor.java:85)
    at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:62)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.base/java.lang.reflect.Method.invoke(Unknown Source)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
    at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
    at jdk.proxy2/jdk.proxy2.$Proxy5.stop(Unknown Source)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker$3.run(TestWorker.java:193)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.executeAndMaintainThreadName(TestWorker.java:129)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:100)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:60)
    at org.gradle.process.internal.worker.child.ActionExecutionWorker.execute(ActionExecutionWorker.java:56)
    at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:113)
    at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:65)
    at worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
    at worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)
kotlin mockk android-jetpack-datastore
Original Q&A
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There are 1 answers

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Moustafa Mesbah On BEST ANSWER

you need to create a flow which is throwing the IO Exception:

@Test
fun `If the data store throws an IOException, it is suppressed and Unknown is returned`() = runTest {
    //given
    val dataFlow: Flow<Preferences> = flow{
        throw IOException()
    }
    coEvery { mockDataStore.data} returns dataFlow
    sut = HubConfigurationLocalDataSource(mockDataStore)

    //expect
    assertEquals(HubConfigurationStatusOnRemote.NOT_FOUND, sut.configurationStatus.first())
}

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