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Mohit Sarveiya Unit Testing Kotlin Channels & Flows www.twitter.com/heyitsmohit www.codingwithmohit.com

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Unit Test Kotlin Channels & Flows ● Use case with ViewModel & Repo ● Testing Repo & ViewModel ● Flow Assertions ● Test Pattern used in Coroutine Library

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Repository Flow View Model

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/users/{id} User Details

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API Service interface ApiService { @GET("/users/{id}") suspend fun userDetails(@Path("id") id: Int): UserDetails }

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Repository class UserRepository(val apiService: ApiService) { fun userDetails(id: Int): Flow> { } } How do we create this Flow?

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fun userDetails(id: Int): Flow> { } fun flow( block: suspend FlowCollector.() "-> Unit ): Flow Creating Flow Coroutine Library

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fun userDetails(id: Int): Flow> { } interface FlowCollector { suspend fun emit(value: T) } Coroutine Library Creating Flow

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Creating Flow fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } }

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Creating Flow fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } } separate thread?

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Creating Flow fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } } Coroutine Library fun Flow.flowOn(context: CoroutineContext): Flow

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Creating Flow fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } } Coroutine Library Dispatcher • Default, IO, Main, etc""...

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Creating Flow class UserRepository( val apiService: ApiService, val dispatcher: CoroutineDispatcher ) { fun userDetails(id: Int): Flow> { return flow { val users = apiService.userDetails(id) emit(Result.success(users)) }.flowOn(dispatcher) }

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Creating Flow class UserRepository( val apiService: ApiService, val dispatcher: CoroutineDispatcher ) { fun userDetails(id: Int): Flow> { return flow { val users = apiService.userDetails(id) emit(Result.success(users)) }.flowOn(dispatcher) }

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Repository Flow View Model View Model

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View Model class UserDetailViewModel : ViewModel { }

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View Model class UserDetailViewModel : ViewModel { val scope = CoroutineScope(Dispatchers.Main) } Coroutine Library fun CoroutineScope(context: CoroutineContext)

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View Model class UserDetailViewModel : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { } }

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View Model class UserDetailViewModel( val repository: UserRepository ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { } }

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View Model class UserDetailViewModel( val repository: UserRepository ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { val flow = repository.getUserDetails(id = 1) } }

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View Model class UserDetailViewModel( val repository: UserRepository ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { val flow = repository.getUserDetails(id = 1) } } Coroutine Library fun Flow.collect( action: suspend (value: T) "-> Unit )

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View Model class UserDetailViewModel( val repository: UserRepository ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> } }

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View Model class UserDetailViewModel( val repository: UserRepository val reducer: Reducer ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> reducer.dispatchState(result) } }

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View Model class UserDetailViewModel( val repository: UserRepository, val reducer: Reducer ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> reducer.dispatchState(result) } }

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val ViewModel.viewModelScope: CoroutineScope get() { val scope: CoroutineScope? = this.getTag(JOB_KEY) return scope } View Model class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) Architecture Components

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Repository Flow View Model

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Kotlin Coroutines Test Library • Test Coroutine Scope • Test Coroutine Dispatcher • runBlockingTest testImplementation ‘org.jetbrains.kotlinx:kotlinx-coroutines-test:x.x.x'

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Unit Test Repository Cases • Flow emits Success • Flow emits Error • Retries with delay (Advanced)

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Repository class UserRepository( val apiService: ApiService, val dispatcher: CoroutineDispatcher ) { fun userDetails(id: Int): Flow> { return flow { val users = apiService.userDetails(id) emit(Result.success(users)) }.flowOn(dispatcher) }

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@Test fun `should get users details on success`() = runBlocking { } Coroutine Library RunBlocking • Creates a coroutine • Blocks until coroutine completes

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@Test fun `should get users details on success`() = runBlocking { val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock() } suspend fun userDetails(id: Int): UserDetails API Service

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@Test fun `should get users details on success`() = runBlocking { val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock() { on { userDetails(1) } doReturn userDetails } Error: Suspend functions can only be called from suspend functions

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@Test fun `should get users details on success`() = runBlocking { val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock() { on { userDetails(1) } doReturn userDetails } } Mockito Kotlin fun on(methodCall: T.() "-> R)

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Mockito Kotlin fun onBlocking(m: suspend T.() "-> R) { return runBlocking { Mockito.`when`(mock.m()) } } @Test fun `should get users details on success`() = runBlocking { val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock() { on { userDetails(1) } doReturn userDetails } }

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@Test fun `should get users details on success`() = runBlocking { val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock() { onBlocking { userDetails(1) } doReturn userDetails } }

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@Test fun `should get users details on success`() = runBlocking { val userDetails = mockUserDetails() }

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@Test fun `should get users details on success`() = runBlocking { val userDetails = mockUserDetails() val dispatcher = TestCoroutineDispatcher() val repository = UserRepository(userService, dispatcher) val flow = repository.getUserDetails(id = 1) }

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@Test fun `should get users details on success`() = runBlocking { val userDetails = mockUserDetails() val dispatcher = TestCoroutineDispatcher() val repository = UserRepository(userService, dispatcher) val flow = repository.getUserDetails(id = 1) val result = flow.single() result.isSuccess.assertTrue() }

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Unit Test Repository Cases • Flow emits Success • Flow emits Error • Retries with delay (Advanced)

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.flowOn(dispatcher) } Exception

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View Model scope.launch { val flow: = userRepository.getUserDetails(id = 1) flow.collect { } } fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.flowOn(dispatcher) } Exception

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.flowOn(dispatcher) } Coroutine Library fun Flow.catch( action: suspend FlowCollector.(t: Throwable) "-> Unit ): Flow

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Exception

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Exception

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@Test fun `should get error for user details`() = runBlocking { val apiService = mock { onBlocking { userDetails(1) } doAnswer { throw IOException() } } } Mock

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@Test fun `should get error for user details`() = runBlocking { val apiService = mockApiService() val repository = UserRepository(apiService, dispatcher) val flow = repository.getUserDetails(id = 1) }

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@Test fun `should get error for user details`() = runBlocking { val apiService = mockApiService() val repository = UserRepository(apiService, dispatcher) val flow = repository.getUserDetails(id = 1) val result = flow.single() result.isFailure.assertTrue() }

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Unit Test Repository Cases • Flow emits Success • Flow emits Error • Retries with delay (Advanced)

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/users/{id} Failed

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/users/{id} - 2 Retries

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Exception

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Coroutine Library fun retry( retries: Long, block: suspend (Throwable) "-> Boolean ): Flow

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) }

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.catch { emit(Result.failure(it)) } .retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Exception

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.catch { emit(Result.failure(it)) } .retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Retry

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.catch { emit(Result.failure(it)) } .retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Delay 1s

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.catch { emit(Result.failure(it)) } .retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Retry

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) }

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Unit Test Retry Cases • All Retries fail with Error • Retry succeeds

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runBlockingTest 1. Launch a coroutine with a test scope and test dispatcher. 2. Advance virtual time forward.

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@Test fun `should retry with error`() { } Coroutine Library fun runBlockingTest( block: suspend TestCoroutineScope.() "-> Unit ) fun TestCoroutineDispatcher.runBlockingTest( block: suspend TestCoroutineScope.() "-> Unit )

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val dispatcher = TestCoroutineDispatcher() @Test fun `should retry with error`() = dispatcher.runBlockingTest { } Create coroutines with test dispatcher

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@Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mock { onBlocking { userDetails(1) } doAnswer { throw IOException() } } }

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@Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mockApiService() val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> result.isFailure.assertTrue() } }

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@Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mockApiService() val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> result.isFailure.assertTrue() } } runBlockingTest

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@Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mockApiService() val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> result.isFailure.assertTrue() } } runBlockingTest

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } runBlockingTest

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } runBlockingTest

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fun userDetails(id: Int): Flow> { return flow { val users = userService.userDetails(id) emit(Result.success(users)) }.retry(retries = 2) { t "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } runBlockingTest Coroutines Test Library fun runBlockingTest { dispatcher.advanceUntilIdle() }

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) runBlockingTest

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Catch Error. All retries failed.

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@Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mockApiService() val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> result.isFailure.assertTrue() } }

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Unit Test Retry Cases • All Retries fail with Error • Retry succeeds

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Retry

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Success

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runBlockingTest Features • Pause Dispatcher • Advance virtual time forward by certain milliseconds.

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { var throwError = true } Control API Response

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { var throwError = true val userDetails = UserDetails(1, "User 1", "avatar_url") } Successful Response

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { var throwError = true val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock { } }

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { var throwError = true val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock { onBlocking { userDetails(1) } doAnswer { if (throwError) throw IOException() else userDetails } } } Control API Response

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { val apiService = mockApiService() pauseDispatcher { } } Coroutine Test Library pausedDispatcher • Do not start coroutines eagerly

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { val apiService = mockApiService() pauseDispatcher { val flow = repository.getUserDetails(id = 1) launch { flow.collect { it.isSuccess.assertTrue() } } } Consumer

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Run Flow

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Suspend

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { val apiService = mockApiService() pauseDispatcher { val flow = repository.getUserDetails(id = 1) launch { flow.collect { it.isSuccess.assertTrue() } } advanceTimeBy(DELAY_ONE_SECOND) } } Advance virtual time

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Retry

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Suspend

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { val apiService = mockApiService() pauseDispatcher { val flow = repository.getUserDetails(id = 1) launch { flow.collect { it.isSuccess.assertTrue() } } advanceTimeBy(DELAY_ONE_SECOND) throwError = false } } Return success

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { val apiService = mockApiService() pauseDispatcher { val flow = repository.getUserDetails(id = 1) launch { flow.collect { it.isSuccess.assertTrue() } } advanceTimeBy(DELAY_ONE_SECOND) throwError = false advanceTimeBy(DELAY_ONE_SECOND) } } Advance virtual time

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Retry

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fun userDetails(id: Int): Flow> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.retry(retries = 2) { t: Throwable "-> (t is Exception).also { if (it) delay(DELAY_ONE_SECOND) } } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Emit Success

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { val apiService = mockApiService() pauseDispatcher { val flow = repository.getUserDetails(id = 1) launch { flow.collect { it.isSuccess.assertTrue() } } advanceTimeBy(DELAY_ONE_SECOND) throwError = false advanceTimeBy(DELAY_ONE_SECOND) } } Collect

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@Test fun `should retry with success`() = dispatcher.runBlockingTest { val apiService = mockApiService() pauseDispatcher { val flow = repository.getUserDetails(id = 1) launch { flow.collect { it.isSuccess.assertTrue() } } advanceTimeBy(DELAY_ONE_SECOND) throwError = false advanceTimeBy(DELAY_ONE_SECOND) } }

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Unit Test Repository Cases • Flow emits Success • Flow emits Error • Retries with delay

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Unit Test View Model Repository Flow View Model

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View Model class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> stateManager.dispatchState(result) } } }

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View Model class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> stateManager.dispatchState(result) } } } Main Dispatcher

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Setting Main Dispatcher • Dispatchers.setMain() • Dispatchers.resetMain()

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Test Rule class CoroutineTestRule( val dispatcher= TestCoroutineDispatcher() ) : TestWatcher() { override fun starting(description: Description?) { super.starting(description) Dispatchers.setMain(dispatcher) } }

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Test Rule class CoroutineTestRule( val dispatcher= TestCoroutineDispatcher() ) : TestWatcher() { override fun finished(description: Description?) { super.finished(description) Dispatchers.resetMain() dispatcher.cleanupTestCoroutines() } }

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View Model Test @get:Rule val rule = CoroutineTestRule()

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View Model Test @get:Rule val rule = CoroutineTestRule() val repository = mock() val stateManager = mock() val viewModel = UserDetailsViewModel(repository, stateManager)

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@Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { } Create coroutine with TestDispatcher

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class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> stateManager.dispatchState(result) } } } Mock Repo

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class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> stateManager.dispatchState(result) } } } Trigger Flow Collection

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View Model Test Flow Send Channel Convert to Flow Receive

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@Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val userDetails = UserDetails(1, "User 1", "avatar") val result = Result.success(userDetails) }

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@Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val userDetails = UserDetails(1, "User 1", "avatar") val result = Result.success(userDetails) val channel = Channel>() } Channel

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@Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val userDetails = UserDetails(1, "User 1", "avatar") val result = Result.success(userDetails) val channel = Channel>() val flow = channel.consumeAsFlow() } Convert to Flow Flow Channel Convert to Flow

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@Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val userDetails = UserDetails(1, "User 1", "avatar") val result = Result.success(userDetails) val channel = Channel>() val flow = channel.consumeAsFlow() whenever(repository.getUserDetails(id = 1)) doReturn flow } Return Flow from Channel

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@Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val result = mockUserDetailsResult() val channel = Channel>() val flow = channel.consumeAsFlow() whenever(repository.getUserDetails(id = 1)) doReturn flow launch { channel.send(result) } } Producer to send values

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@Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val result = mockUserDetailsResult() val channel = Channel>() val flow = channel.consumeAsFlow() whenever(repository.getUserDetails(id = 1)) doReturn flow launch { channel.send(result) } userDetailsViewModel.getUserDetails() } Run test method

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class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result "-> stateManager.dispatchState(result) } } } Collect result from Flow

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@Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val result = mockUserDetailsResult() val channel = Channel>() val flow = channel.consumeAsFlow() whenever(repository.getUserDetails(id = 1)) doReturn flow launch { channel.send(result) } userDetailsViewModel.getUserDetails() verify(stateManager).dispatch(result) } Verify result

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Repository Flow View Model

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Flow Assertions @Test fun `should get users details on success`() = runBlocking { ""... flow.collect { } flow.single() } RxJava Observable.test()

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Flow Assertions API fun expectItem(): T fun expectNoMoreEvents() fun expectComplete() fun expectError(): Throwable Test Flow Channel

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sealed class Event { object Complete : Event() data class Error(val t: Throwable) : Event() data class Item(val item: T) : Event() } Flow Assertions Test Flow Channel

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Flow Assertions sealed class Event { object Complete : Event() data class Error(val t: Throwable) : Event() data class Item(val item: T) : Event() } Item Test Flow Channel

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Flow Assertions sealed class Event { object Complete : Event() data class Error(val t: Throwable) : Event() data class Item(val item: T) : Event() } Test Flow Channel Flow emission complete

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sealed class Event { object Complete : Event() data class Error(val t: Throwable) : Event() data class Item(val item: T) : Event() } Flow Assertions Test Flow Channel Error

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Flow Assertions suspend fun Flow.test( validate: suspend FlowAssert.() "-> Unit ) { }

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Flow Assertions suspend fun Flow.test( validate: suspend FlowAssert.() "-> Unit ) { coroutineScope { val events = Channel>(UNLIMITED) } } Unlimited Buffered Channel

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Flow Assertions suspend fun Flow.test( validate: suspend FlowAssert.() "-> Unit ) { coroutineScope { val events = Channel>(UNLIMITED) launch { collect { item "-> events.send(Event.Item(item)) } Event.Complete } } } Send to Channel

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Flow Assertions suspend fun Flow.test( validate: suspend FlowAssert.() "-> Unit ) { coroutineScope { val events = Channel>(UNLIMITED) launch { try { sendToChannel() } catch (t: Throwable) { send(Event.Error(t)) } } } } Send Error

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Flow Assertions suspend fun Flow.test( validate: suspend FlowAssert.() "-> Unit ) { coroutineScope { val events = Channel>(UNLIMITED) launch { collect { item "-> events.send(Event.Item(item)) } Event.Complete } } }

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Flow Assertions class FlowAssert(val events: Channel>) { suspend fun expectItem(): T suspend fun expectComplete() suspend fun expectError(): Throwable … }

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Flow Assertions @Test fun `should get users details on success`() = runBlocking { flow.test { expectItem() assertEquals userDetails expectComplete() } }

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Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Expect

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Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Finish

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Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Test Base

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Kotlin Coroutines Library Testing expect open class TestBase { fun error(message: Any, cause: Throwable? = null): Nothing fun expect(index: Int) fun finish(index: Int) fun runTest( expected: ((Throwable) "-> Boolean)? = null, unhandled: List<(Throwable) "-> Boolean> = emptyList(), block: suspend CoroutineScope.() "-> Unit )

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Kotlin Coroutines Library Testing JVM JS Native Common TestBase.kt TestBase.kt TestBase.kt TestBase.kt

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Kotlin Coroutines Library Testing actual open class TestBase actual constructor() { actual fun runTest( expected: ((Throwable) "-> Boolean)? = null, unhandled: List<(Throwable) "-> Boolean> = emptyList(), block: suspend CoroutineScope.() "-> Unit ) { runBlocking( block = block, context = CoroutineExceptionHandler { }) }

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Kotlin Coroutines Library Testing actual open class TestBase actual constructor() { actual fun runTest( expected: ((Throwable) "-> Boolean)? = null, unhandled: List<(Throwable) "-> Boolean> = emptyList(), block: suspend CoroutineScope.() "-> Unit ) { runBlocking( block = block, context = CoroutineExceptionHandler { }) }

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Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Expect

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Kotlin Coroutines Library Testing private var actionIndex = AtomicInteger() actual fun expect(index: Int) { val wasIndex = actionIndex.incrementAndGet() if (VERBOSE) println("expect($index), wasIndex=$wasIndex") check(index "== wasIndex) { “Expecting action index $index but it is actually $wasIndex" } }

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Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Finish

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Kotlin Coroutines Library Testing private var finished = AtomicBoolean() actual fun finish(index: Int) { expect(index) check(!finished.getAndSet(true)) { "Should call 'finish(""...)' at most once" } }

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Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } }

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Resources ● Unit Testing Delays, Errors & Retries with Kotlin Flows https:"//codingwithmohit.com/coroutines/unit-testing-delays- errors-retries-with-kotlin-flows/ ● Kotlin Assert Flow Delight https:"//codingwithmohit.com/coroutines/kotlin-assert-flow-delight/ ● Channels & Flows in Practice https:"//speakerdeck.com/heyitsmohit/channels-and-flows-in-practice

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Thank You! www.twitter.com/heyitsmohit www.codingwithmohit.com