title: TimeoutCancellationException when running tests for a Retrofit coroutine in a Kotlin flow
body: <p>I have a repository that creates a flow where I emit the result of a suspending Retrofit method. This works in the app, but I would like to run tests on the code.</p>
  <p>I am using kotlinx-coroutines-test v1.6.0 and MockWebServer v4.9.3 in my tests. When I try to run a test, I get:</p>
  <pre><code>Timed out waiting for 1000 ms
  kotlinx.coroutines.TimeoutCancellationException: Timed out waiting for 1000 ms
      at app//kotlinx.coroutines.TimeoutKt.TimeoutCancellationException(Timeout.kt:184)
      at app//kotlinx.coroutines.TimeoutCoroutine.run(Timeout.kt:154)
      at app//kotlinx.coroutines.test.TestDispatcher.processEvent$kotlinx_coroutines_test(TestDispatcher.kt:23)
      at app//kotlinx.coroutines.test.TestCoroutineScheduler.tryRunNextTask(TestCoroutineScheduler.kt:95)
      at app//kotlinx.coroutines.test.TestCoroutineScheduler.advanceUntilIdle(TestCoroutineScheduler.kt:110)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt.runTestCoroutine(TestBuilders.kt:212)
      at app//kotlinx.coroutines.test.TestBuildersKt.runTestCoroutine(Unknown Source)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt$runTest$1$1.invokeSuspend(TestBuilders.kt:167)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt$runTest$1$1.invoke(TestBuilders.kt)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt$runTest$1$1.invoke(TestBuilders.kt)
      at app//kotlinx.coroutines.test.TestBuildersJvmKt$createTestResult$1.invokeSuspend(TestBuildersJvm.kt:13)
      (Coroutine boundary)
      at app.cash.turbine.ChannelBasedFlowTurbine$awaitEvent$2.invokeSuspend(FlowTurbine.kt:247)
      at app.cash.turbine.ChannelBasedFlowTurbine$withTimeout$2.invokeSuspend(FlowTurbine.kt:215)
      at app.cash.turbine.ChannelBasedFlowTurbine.awaitItem(FlowTurbine.kt:252)
      at ogbe.eva.prompt.home.HomeRepositoryTest$currentTask when server responds with error emits failure$1$1.invokeSuspend(HomeRepositoryTest.kt:90)
      at app.cash.turbine.FlowTurbineKt$test$2.invokeSuspend(FlowTurbine.kt:86)
      at ogbe.eva.prompt.home.HomeRepositoryTest$currentTask when server responds with error emits failure$1.invokeSuspend(HomeRepositoryTest.kt:89)
      at kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt$runTestCoroutine$2.invokeSuspend(TestBuilders.kt:208)
      (Coroutine creation stacktrace)
      at app//kotlinx.coroutines.intrinsics.UndispatchedKt.startCoroutineUndispatched(Undispatched.kt:184)
      at app//kotlinx.coroutines.test.TestBuildersJvmKt$createTestResult$1.invokeSuspend(TestBuildersJvm.kt:13)
      at app//kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
      at app//kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt.runTest$default(TestBuilders.kt:161)
      at app//kotlinx.coroutines.test.TestBuildersKt.runTest$default(Unknown Source)
      at app//ogbe.eva.prompt.TestCoroutineRule.runTest(TestCoroutineRule.kt:26)
      at app//ogbe.eva.prompt.home.HomeRepositoryTest.currentTask when server responds with error emits failure(HomeRepositoryTest.kt:84)
      at java.base@11.0.11/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at java.base@11.0.11/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
      at java.base@11.0.11/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.base@11.0.11/java.lang.reflect.Method.invoke(Method.java:566)
      at app//org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
      at app//org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
      at app//org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
      at app//org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
      at app//org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
      at app//org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
      at app//org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:61)
      at app//org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
      at app//org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
      at app//org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
      at app//org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
      at app//org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
      at app//org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
      at app//org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
      at app//org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
      at app//org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
      at app//org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
      at app//org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
      at app//org.junit.runners.ParentRunner.run(ParentRunner.java:413)
      at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.runTestClass(JUnitTestClassExecutor.java:110)
      at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:58)
      at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:38)
      at org.gradle.api.internal.tasks.testing.junit.AbstractJUnitTestClassProcessor.processTestClass(AbstractJUnitTestClassProcessor.java:62)
      at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:51)
      at java.base@11.0.11/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at java.base@11.0.11/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
      at java.base@11.0.11/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.base@11.0.11/java.lang.reflect.Method.invoke(Method.java:566)
      at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
      at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
      at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
      at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
      at com.sun.proxy.$Proxy2.processTestClass(Unknown Source)
      at org.gradle.api.internal.tasks.testing.worker.TestWorker$2.run(TestWorker.java:176)
      at org.gradle.api.internal.tasks.testing.worker.TestWorker.executeAndMaintainThreadName(TestWorker.java:129)
      at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:100)
      at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:60)
      at org.gradle.process.internal.worker.child.ActionExecutionWorker.execute(ActionExecutionWorker.java:56)
      at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:133)
      at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:71)
      at app//worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
      at app//worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)
  Caused by: kotlinx.coroutines.TimeoutCancellationException: Timed out waiting for 1000 ms
      at app//kotlinx.coroutines.TimeoutKt.TimeoutCancellationException(Timeout.kt:184)
      at app//kotlinx.coroutines.TimeoutCoroutine.run(Timeout.kt:154)
      at app//kotlinx.coroutines.test.TestDispatcher.processEvent$kotlinx_coroutines_test(TestDispatcher.kt:23)
      at app//kotlinx.coroutines.test.TestCoroutineScheduler.tryRunNextTask(TestCoroutineScheduler.kt:95)
      at app//kotlinx.coroutines.test.TestCoroutineScheduler.advanceUntilIdle(TestCoroutineScheduler.kt:110)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt.runTestCoroutine(TestBuilders.kt:212)
      at app//kotlinx.coroutines.test.TestBuildersKt.runTestCoroutine(Unknown Source)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt$runTest$1$1.invokeSuspend(TestBuilders.kt:167)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt$runTest$1$1.invoke(TestBuilders.kt)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt$runTest$1$1.invoke(TestBuilders.kt)
      at app//kotlinx.coroutines.test.TestBuildersJvmKt$createTestResult$1.invokeSuspend(TestBuildersJvm.kt:13)
      at app//kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
      at app//kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
      at app//kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:279)
      at app//kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:85)
      at app//kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:59)
      at app//kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)
      at app//kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:38)
      at app//kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)
      at app//kotlinx.coroutines.test.TestBuildersJvmKt.createTestResult(TestBuildersJvm.kt:12)
      at app//kotlinx.coroutines.test.TestBuildersKt__TestBuildersKt.runTest(TestBuilders.kt:166)
      at app//kotlinx.coroutines.test.TestBuildersKt.runTest(Unknown Source)
      ... 50 more
  </code></pre>
  <p>I don't get the chance to run my test assertions, which is what I want to do. It just fails with this unexpected error.</p>
  <p>I have checked with calling random suspending functions in the flow and running the mock server outside of my flow function. Both of those will complete without the timeout error, but when I combine the flow and the test and Retrofit, it shows the timeout error.</p>
  <p>Repository code:</p>
  <pre><code>class HomeRepository @Inject constructor(
      @IoDispatcher ioDispatcher: CoroutineDispatcher,
      private val promptService: PromptService,
  ) {
      val currentTask = flow {
          try {
              val response = promptService.getSchedule(1) // Suspending Retrofit method that fails the tests
              if (response.isSuccessful) {
                  val schedule = response.body()
                  if (schedule == null) {
                      Log.e(TAG, &quot;Get schedule response has empty body&quot;)
                      emit(LoadState.Failure())
                  } else {
                      emit(LoadState.Data(schedule.tasks.first()))
                  }
              } else {
                  Log.e(
                      TAG,
                      &quot;Server responded to get schedule request with error: ${response.message()}&quot;
                  )
                  emit(LoadState.Failure())
              }
          } catch (e: Exception) {
              Log.e(TAG, &quot;Could not get schedule from server&quot;, e)
              emit(LoadState.Failure())
          }
      }
          .flowOn(ioDispatcher)
  
      companion object {
          private val TAG = HomeRepository::class.simpleName
      }
  }
  </code></pre>
  <p>Test code:</p>
  <pre><code>@OptIn(ExperimentalCoroutinesApi::class)
  class HomeRepositoryTest {
      @get:Rule
      val testCoroutineRule = TestCoroutineRule()
  
      private val mockWebServer = MockWebServer()
  
      @Before
      fun setUp() {
          mockWebServer.start()
      }
  
      @After
      fun tearDown() {
          mockWebServer.shutdown()
      }
  
      @Test
      fun `currentTask when server responds with error emits failure`() = testCoroutineRule.runTest {
          mockWebServer.enqueue(MockResponse().setResponseCode(500))
  
          val homeRepository = createRepository()
  
          homeRepository.currentTask.test {
              expectThat(awaitItem()).isFailure()
              awaitComplete()
          }
      }
  
      private fun createRepository(promptService: PromptService = createPromptService()) =
          HomeRepository(testCoroutineRule.testDispatcher, promptService)
  
      private fun createPromptService(): PromptService {
          val client = OkHttpClient.Builder()
              .connectTimeout(1, TimeUnit.SECONDS)
              .readTimeout(1, TimeUnit.SECONDS)
              .writeTimeout(1, TimeUnit.SECONDS)
              .build()
          return Retrofit.Builder()
              .baseUrl(mockWebServer.url(&quot;/&quot;))
              .client(client)
              .addConverterFactory(MoshiConverterFactory.create())
              .build()
              .create(PromptService::class.java)
      }
  }
  </code></pre>
  <p>Rule code:</p>
  <pre><code>@OptIn(ExperimentalCoroutinesApi::class)
  class TestCoroutineRule : TestWatcher() {
      val testDispatcher = StandardTestDispatcher()
  
      private val testScope = TestScope(testDispatcher)
  
      override fun starting(description: Description?) {
          super.starting(description)
          Dispatchers.setMain(testDispatcher)
      }
  
      override fun finished(description: Description?) {
          super.finished(description)
          Dispatchers.resetMain()
      }
  
      fun runTest(block: suspend TestScope.() -&gt; Unit) =
          testScope.runTest(testBody = block)
  }
  </code></pre>
  <p>How do I test a flow that uses Retrofit without getting a timeout error?</p>