Unit Testing Channels & Flows

Unit testing Channels and Flows can be a challenge as they are fairly new. In this talk, I will share with you how to implement and test practical examples from my experience. These examples are testing delays, retries, and errors. I'll also share testing more complex examples such as polling. For each use case, we'll look at how to use features in the coroutines library such as runBlockingTest and TestCoroutineDispatcher. From my journey of using and testing Flows in production, I'll share the challenges I experienced.

https://youtu.be/h8bLIUi6HWU

Transcript

1. Mohit Sarveiya Unit Testing Kotlin Channels & Flows www.twitter.com/heyitsmohit www.codingwithmohit.com
2. Unit Test Kotlin Channels & Flows • Use case with ViewModel & Repo • Testing Repo & ViewModel • Flow Assertions • Test Pattern used in Coroutine Library
3. Repository Flow<UserDetails> View Model
4. /users/{id} User Details
5. API Service interface ApiService { @GET("/users/{id}") suspend fun userDetails(@Path("id") id: Int): UserDetails }
6. Repository class UserRepository(val apiService: ApiService) { fun userDetails(id: Int): Flow<Result<UserDetails">> { } } How do we create this Flow?
7. fun userDetails(id: Int): Flow<Result<UserDetails">> { } fun <T> flow( block: suspend FlowCollector<T>.() "-> Unit ): Flow<T> Creating Flow Coroutine Library
8. fun userDetails(id: Int): Flow<Result<UserDetails">> { } interface FlowCollector<in T> { suspend fun emit(value: T) } Coroutine Library Creating Flow
9. Creating Flow fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } }
10. Creating Flow fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } } separate thread?
11. Creating Flow fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } } Coroutine Library fun Flow<T>.flowOn(context: CoroutineContext): Flow<T>
12. Creating Flow fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } } Coroutine Library Dispatcher • Default, IO, Main, etc""...
13. Creating Flow class UserRepository( val apiService: ApiService, val dispatcher: CoroutineDispatcher ) { fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val users = apiService.userDetails(id) emit(Result.success(users)) }.flowOn(dispatcher) }
14. Creating Flow class UserRepository( val apiService: ApiService, val dispatcher: CoroutineDispatcher ) { fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val users = apiService.userDetails(id) emit(Result.success(users)) }.flowOn(dispatcher) }
15. Repository Flow<UserDetails> View Model View Model
16. View Model class UserDetailViewModel : ViewModel { }
17. View Model class UserDetailViewModel : ViewModel { val scope = CoroutineScope(Dispatchers.Main) } Coroutine Library fun CoroutineScope(context: CoroutineContext)
18. View Model class UserDetailViewModel : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { } }
19. View Model class UserDetailViewModel( val repository: UserRepository ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { } }
20. View Model class UserDetailViewModel( val repository: UserRepository ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { val flow = repository.getUserDetails(id = 1) } }
21. View Model class UserDetailViewModel( val repository: UserRepository ) : ViewModel { val scope = CoroutineScope(Dispatchers.Main) scope.launch { val flow = repository.getUserDetails(id = 1) } } Coroutine Library fun <T> Flow<T>.collect( action: suspend (value: T) "-> Unit )
22. 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<UserDetails> "-> } }
23. 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<UserDetails> "-> reducer.dispatchState(result) } }
24. 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<UserDetails> "-> reducer.dispatchState(result) } }
25. 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
26. Repository Flow<UserDetails> View Model
27. Kotlin Coroutines Test Library • Test Coroutine Scope • Test Coroutine Dispatcher • runBlockingTest testImplementation ‘org.jetbrains.kotlinx:kotlinx-coroutines-test:x.x.x'
28. Unit Test Repository Cases • Flow emits Success • Flow emits Error • Retries with delay (Advanced)
29. Repository class UserRepository( val apiService: ApiService, val dispatcher: CoroutineDispatcher ) { fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val users = apiService.userDetails(id) emit(Result.success(users)) }.flowOn(dispatcher) }
30. @Test fun `should get users details on success`() = runBlocking { } Coroutine Library RunBlocking • Creates a coroutine • Blocks until coroutine completes
31. @Test fun `should get users details on success`() = runBlocking { val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock<ApiService>() } suspend fun userDetails(id: Int): UserDetails API Service
32. @Test fun `should get users details on success`() = runBlocking { val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock<ApiService>() { on { userDetails(1) } doReturn userDetails } Error: Suspend functions can only be called from suspend functions
33. @Test fun `should get users details on success`() = runBlocking { val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock<ApiService>() { on { userDetails(1) } doReturn userDetails } } Mockito Kotlin fun <R> on(methodCall: T.() "-> R)
34. 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<ApiService>() { on { userDetails(1) } doReturn userDetails } }
35. @Test fun `should get users details on success`() = runBlocking { val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock<ApiService>() { onBlocking { userDetails(1) } doReturn userDetails } }
36. @Test fun `should get users details on success`() = runBlocking { val userDetails = mockUserDetails() }
37. @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) }
38. @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() }
39. Unit Test Repository Cases • Flow emits Success • Flow emits Error • Retries with delay (Advanced)
40. fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.flowOn(dispatcher) } Exception
41. View Model scope.launch { val flow: = userRepository.getUserDetails(id = 1) flow.collect { } } fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.flowOn(dispatcher) } Exception
42. fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.flowOn(dispatcher) } Coroutine Library fun <T> Flow<T>.catch( action: suspend FlowCollector<T>.(t: Throwable) "-> Unit ): Flow<T>
43. fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Exception
44. fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Exception
45. @Test fun `should get error for user details`() = runBlocking { val apiService = mock<ApiService> { onBlocking { userDetails(1) } doAnswer { throw IOException() } } } Mock
46. @Test fun `should get error for user details`() = runBlocking { val apiService = mockApiService() val repository = UserRepository(apiService, dispatcher) val flow = repository.getUserDetails(id = 1) }
47. @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() }
48. Unit Test Repository Cases • Flow emits Success • Flow emits Error • Retries with delay (Advanced)
49. /users/{id} Failed
50. /users/{id} - 2 Retries
51. fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) }.catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Exception
52. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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<T>
53. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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) }
54. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
55. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
56. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
57. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
58. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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) }
59. Unit Test Retry Cases • All Retries fail with Error • Retry succeeds
60. runBlockingTest 1. Launch a coroutine with a test scope and test dispatcher. 2. Advance virtual time forward.
61. @Test fun `should retry with error`() { } Coroutine Library fun runBlockingTest( block: suspend TestCoroutineScope.() "-> Unit ) fun TestCoroutineDispatcher.runBlockingTest( block: suspend TestCoroutineScope.() "-> Unit )
62. val dispatcher = TestCoroutineDispatcher() @Test fun `should retry with error`() = dispatcher.runBlockingTest { } Create coroutines with test dispatcher
63. @Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mock<ApiService> { onBlocking { userDetails(1) } doAnswer { throw IOException() } } }
64. @Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mockApiService() val flow = repository.getUserDetails(id = 1) flow.collect { result: Result<UserDetails> "-> result.isFailure.assertTrue() } }
65. @Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mockApiService() val flow = repository.getUserDetails(id = 1) flow.collect { result: Result<UserDetails> "-> result.isFailure.assertTrue() } } runBlockingTest
66. @Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mockApiService() val flow = repository.getUserDetails(id = 1) flow.collect { result: Result<UserDetails> "-> result.isFailure.assertTrue() } } runBlockingTest
67. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
68. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
69. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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() }
70. fun userDetails(id: Int): Flow<Result<UserDetails">> { return flow { val userDetails = apiService.userDetails(id) emit(Result.success(userDetails)) runBlockingTest
71. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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.
72. @Test fun `should retry with error`() = dispatcher.runBlockingTest { val apiService = mockApiService() val flow = repository.getUserDetails(id = 1) flow.collect { result: Result<UserDetails> "-> result.isFailure.assertTrue() } }
73. Unit Test Retry Cases • All Retries fail with Error • Retry succeeds
74. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
75. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
76. runBlockingTest Features • Pause Dispatcher • Advance virtual time forward by certain milliseconds.
77. @Test fun `should retry with success`() = dispatcher.runBlockingTest { var throwError = true } Control API Response
78. @Test fun `should retry with success`() = dispatcher.runBlockingTest { var throwError = true val userDetails = UserDetails(1, "User 1", "avatar_url") } Successful Response
79. @Test fun `should retry with success`() = dispatcher.runBlockingTest { var throwError = true val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock<ApiService> { } }
80. @Test fun `should retry with success`() = dispatcher.runBlockingTest { var throwError = true val userDetails = UserDetails(1, "User 1", "avatar_url") val apiService = mock<ApiService> { onBlocking { userDetails(1) } doAnswer { if (throwError) throw IOException() else userDetails } } } Control API Response
81. @Test fun `should retry with success`() = dispatcher.runBlockingTest { val apiService = mockApiService() pauseDispatcher { } } Coroutine Test Library pausedDispatcher • Do not start coroutines eagerly
82. @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
83. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
84. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
85. @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
86. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
87. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
88. @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
89. @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
90. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
91. fun userDetails(id: Int): Flow<Result<UserDetails">> { 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
92. @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
93. @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) } }
94. Unit Test Repository Cases • Flow emits Success • Flow emits Error • Retries with delay
95. Unit Test View Model Repository Flow<UserDetails> View Model
96. View Model class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result<UserDetails> "-> stateManager.dispatchState(result) } } }
97. View Model class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result<UserDetails> "-> stateManager.dispatchState(result) } } } Main Dispatcher
98. Setting Main Dispatcher • Dispatchers.setMain() • Dispatchers.resetMain()
99. Test Rule class CoroutineTestRule( val dispatcher= TestCoroutineDispatcher() ) : TestWatcher() { override fun starting(description: Description?) { super.starting(description) Dispatchers.setMain(dispatcher) } }
100. Test Rule class CoroutineTestRule( val dispatcher= TestCoroutineDispatcher() ) : TestWatcher() { override fun finished(description: Description?) { super.finished(description) Dispatchers.resetMain() dispatcher.cleanupTestCoroutines() } }
101. View Model Test @get:Rule val rule = CoroutineTestRule()
102. View Model Test @get:Rule val rule = CoroutineTestRule() val repository = mock<UserRepository>() val stateManager = mock<StateManager>() val viewModel = UserDetailsViewModel(repository, stateManager)
103. @Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { } Create coroutine with TestDispatcher
104. class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result<UserDetails> "-> stateManager.dispatchState(result) } } } Mock Repo
105. class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result<UserDetails> "-> stateManager.dispatchState(result) } } } Trigger Flow Collection
106. View Model Test Flow Send Channel Convert to Flow Receive
107. @Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val userDetails = UserDetails(1, "User 1", "avatar") val result = Result.success(userDetails) }
108. @Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val userDetails = UserDetails(1, "User 1", "avatar") val result = Result.success(userDetails) val channel = Channel<Result<UserDetails">>() } Channel
109. @Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val userDetails = UserDetails(1, "User 1", "avatar") val result = Result.success(userDetails) val channel = Channel<Result<UserDetails">>() val flow = channel.consumeAsFlow() } Convert to Flow Flow Channel Convert to Flow
110. @Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val userDetails = UserDetails(1, "User 1", "avatar") val result = Result.success(userDetails) val channel = Channel<Result<UserDetails">>() val flow = channel.consumeAsFlow() whenever(repository.getUserDetails(id = 1)) doReturn flow } Return Flow from Channel
111. @Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val result = mockUserDetailsResult() val channel = Channel<Result<UserDetails">>() val flow = channel.consumeAsFlow() whenever(repository.getUserDetails(id = 1)) doReturn flow launch { channel.send(result) } } Producer to send values
112. @Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val result = mockUserDetailsResult() val channel = Channel<Result<UserDetails">>() val flow = channel.consumeAsFlow() whenever(repository.getUserDetails(id = 1)) doReturn flow launch { channel.send(result) } userDetailsViewModel.getUserDetails() } Run test method
113. class UserDetailViewModel( val repository: UserRepository, val stateManager: StateManager ) : ViewModel { viewModelScope.launch { val flow = repository.getUserDetails(id = 1) flow.collect { result: Result<UserDetails> "-> stateManager.dispatchState(result) } } } Collect result from Flow
114. @Test fun `should dispatch details`() = rule.dispatcher.runBlockingTest { val result = mockUserDetailsResult() val channel = Channel<Result<UserDetails">>() val flow = channel.consumeAsFlow() whenever(repository.getUserDetails(id = 1)) doReturn flow launch { channel.send(result) } userDetailsViewModel.getUserDetails() verify(stateManager).dispatch(result) } Verify result
115. Repository Flow<UserDetails> View Model
116. Flow Assertions @Test fun `should get users details on success`() = runBlocking { ""... flow.collect { } flow.single() } RxJava Observable.test()
118. Flow Assertions API fun expectItem(): T fun expectNoMoreEvents() fun expectComplete() fun expectError(): Throwable Test Flow Channel
119. sealed class Event<out T> { object Complete : Event<Nothing>() data class Error(val t: Throwable) : Event<Nothing>() data class Item<T>(val item: T) : Event<T>() } Flow Assertions Test Flow Channel
120. Flow Assertions sealed class Event<out T> { object Complete : Event<Nothing>() data class Error(val t: Throwable) : Event<Nothing>() data class Item<T>(val item: T) : Event<T>() } Item Test Flow Channel
121. Flow Assertions sealed class Event<out T> { object Complete : Event<Nothing>() data class Error(val t: Throwable) : Event<Nothing>() data class Item<T>(val item: T) : Event<T>() } Test Flow Channel Flow emission complete
122. sealed class Event<out T> { object Complete : Event<Nothing>() data class Error(val t: Throwable) : Event<Nothing>() data class Item<T>(val item: T) : Event<T>() } Flow Assertions Test Flow Channel Error
123. Flow Assertions suspend fun <T> Flow<T>.test( validate: suspend FlowAssert<T>.() "-> Unit ) { }
124. Flow Assertions suspend fun <T> Flow<T>.test( validate: suspend FlowAssert<T>.() "-> Unit ) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) } } Unlimited Buffered Channel
125. Flow Assertions suspend fun <T> Flow<T>.test( validate: suspend FlowAssert<T>.() "-> Unit ) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) launch { collect { item "-> events.send(Event.Item(item)) } Event.Complete } } } Send to Channel
126. Flow Assertions suspend fun <T> Flow<T>.test( validate: suspend FlowAssert<T>.() "-> Unit ) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) launch { try { sendToChannel() } catch (t: Throwable) { send(Event.Error(t)) } } } } Send Error
127. Flow Assertions suspend fun <T> Flow<T>.test( validate: suspend FlowAssert<T>.() "-> Unit ) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) launch { collect { item "-> events.send(Event.Item(item)) } Event.Complete } } }
128. Flow Assertions class FlowAssert<T>(val events: Channel<Event<T">>) { suspend fun expectItem(): T suspend fun expectComplete() suspend fun expectError(): Throwable … }
129. Flow Assertions @Test fun `should get users details on success`() = runBlocking { flow.test { expectItem() assertEquals userDetails expectComplete() } }
132. Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Expect
133. Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Finish
134. Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Test Base
135. 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 )
136. Kotlin Coroutines Library Testing JVM JS Native Common TestBase.kt TestBase.kt TestBase.kt TestBase.kt
137. 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 { }) }
138. 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 { }) }
139. Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Expect
140. 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" } }
141. Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } } Finish
142. 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" } }
143. Kotlin Coroutines Library Testing class CoroutinesTest : TestBase() { @Test fun testSimple() = runTest { expect(1) finish(2) } }
144. 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
145. Thank You! www.twitter.com/heyitsmohit www.codingwithmohit.com