Unit Testing Kotlin Channels & Flows - DevFest UK & Ireland 2020

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.

Transcript

1. Mohit Sarveiya Unit Testing Kotlin Channels & Flows www.twitter.com/heyitsmohit www.codingwithmohit.com
2. Unit Testing Channels & Flows • Run Blocking Test • Flow Test Cases • Flow Assertions with Turbine • View Model Testing
3. Flow Test Cases
4. Flow Test Cases • Collection • Run on Dispatcher • Errors • Retries Fail • Retry Succeeds
7. GraphQL gRPC REST
9. Flow of users
10. User(1, "User 1", “UK")
11. Repository Service Flow of users
12. class UsersRepository() { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== "NYC" } .map { it.name } } }
13. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== "NYC" } .map { it.name } } }
14. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== "NYC" } .map { it.name } } }
15. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== "NYC" } .map { it.name } } } Flow of Users
16. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== “UK" } .map { it.name } } } Filter users
17. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== “UK" } .map { it.name } } } Map user name
18. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== “UK" } .map { it.name } } } How do we test this Flow?
19. Kotlin/kotlinx.coroutines Code ! Issues Pull Requests kotlinx-coroutines-core 2,093 commits 4c28f942 13 hours ago Kotlinx-coroutines-debug Kotlinx-coroutines-test reactive js benchmarks
20. Kotlin/kotlinx.coroutines Code ! Issues Pull Requests kotlinx-coroutines-core 2,093 commits 4c28f942 13 hours ago Kotlinx-coroutines-debug Kotlinx-coroutines-test reactive js benchmarks Testing Module
21. Kotlin/kotlinx.coroutines Code ! Issues Pull Requests README.md Module Kotlin-coroutines-test Test utilities for kotlinx.coroutines dependencies { testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.3.9' }
22. @Test fun `should get users`() { }
23. @Test fun `should get users`() = runBlockingTest { } Creates a coroutine
24. @Test fun `should get users`() = runBlockingTest { } Test Scope
25. @Test fun `should get users`() = runBlockingTest { } Test Scope + Test Dispatcher
26. @Test fun `should get users`() = runBlockingTest { } Test Scope + Test Dispatcher What is executed in this coroutine?
27. @Test fun `should get users`() = runBlockingTest { } Test Scope + Test Dispatcher
28. @Test fun `should get users`() = runBlockingTest { } Test Scope + Test Dispatcher
29. fun runBlockingTest(testBody) { val scope = TestCoroutineScope(safeContext) val deferred = scope.async { scope.testBody() } deferred.getCompletionExceptionOrNull()"?.let { throw it } scope.cleanupTestCoroutines() if (hasActiveJobs()) { throw UncompletedCoroutinesError("Test finished with active jobs: $endingJobs") } } Our test to run
30. fun runBlockingTest(testBody) { val scope = TestCoroutineScope(safeContext) val deferred = scope.async { scope.testBody() } deferred.getCompletionExceptionOrNull()"?.let { throw it } scope.cleanupTestCoroutines() if (hasActiveJobs()) { throw UncompletedCoroutinesError("Test finished with active jobs: $endingJobs") } } Test Coroutine Scope
31. fun runBlockingTest(testBody) { val scope = TestCoroutineScope(safeContext) val deferred = scope.async { scope.testBody() } deferred.getCompletionExceptionOrNull()"?.let { throw it } scope.cleanupTestCoroutines() if (hasActiveJobs()) { throw UncompletedCoroutinesError("Test finished with active jobs: $endingJobs") } } Wrap your test in Deferred
32. fun runBlockingTest(testBody) { val scope = TestCoroutineScope(safeContext) val deferred = scope.async { scope.testBody() } deferred.getCompletionExceptionOrNull()"?.let { throw it } scope.cleanupTestCoroutines() if (hasActiveJobs()) { throw UncompletedCoroutinesError("Test finished with active jobs: $endingJobs") } } Run your test!
33. fun runBlockingTest(testBody) { val scope = TestCoroutineScope(safeContext) val deferred = scope.async { scope.testBody() } deferred.getCompletionExceptionOrNull()"?.let { throw it } scope.cleanupTestCoroutines() if (hasActiveJobs()) { throw UncompletedCoroutinesError("Test finished with active jobs: $endingJobs") } } Cancel all Jobs in test
34. fun runBlockingTest(testBody) { val scope = TestCoroutineScope(safeContext) val deferred = scope.async { scope.testBody() } deferred.getCompletionExceptionOrNull()"?.let { throw it } scope.cleanupTestCoroutines() if (hasActiveJobs()) { throw UncompletedCoroutinesError("Test finished with active jobs: $endingJobs") } } Fail on active coroutines
35. fun runBlockingTest(testBody) { val scope = TestCoroutineScope(safeContext) val deferred = scope.async { scope.testBody() } deferred.getCompletionExceptionOrNull()"?.let { throw it } scope.cleanupTestCoroutines() if (activeJobs()).isNotEmpty()) { throw UncompletedCoroutinesError("Test finished with active jobs") } } Setup Run Test Cleanup
36. @Test fun `should get users`() = runBlockingTest { }
37. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== “UK" } .map { it.name } } } How do we mock service?
38. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== “UK" } .map { it.name } } } Mock or Create fake
39. nhaarman/mockito-kotlin Code ! Issues Pull Requests Mockito-Kotlin A small library that provides helper functions to work with Mockito in Kotlin. maven central 2.2.0
40. val apiService = mock<ApiService> { on { getUsers() } doReturn users.asFlow() } @Test fun `should get users`() = runBlockingTest { } Mock API Service
41. val apiService = mock<ApiService> { on { getUsers() } doReturn users.asFlow() } @Test fun `should get users`() = runBlockingTest { } Return a Flow of users
42. val apiService = mock<ApiService> { on { getUsers() } doReturn users.asFlow() } @Test fun `should get users`() = runBlockingTest { } val users = listOf( User(1, "User 1", “NYC"), User(2, "User 2", "UK"), User(3, "User 3", "CA"), User(4, "User 4", “NYC"), User(5, "User 5", "UK") )
43. val apiService = mock<ApiService> { on { getUsers() } doReturn users.asFlow() } @Test fun `should get users`() = runBlockingTest { } User(1, "User 1", “NYC”)
44. val apiService = mock<ApiService> { on { getUsers() } doReturn users.asFlow() } val usersRepository = UsersRepository(apiService) fun `should get users`() = runBlockingTest { } Inject mock into Repo
45. @Test fun `should get users`() = runBlockingTest { val usersList = usersRepository.getUsers().toList() assertEquals(users, listOf("User 2", "User 5")) } Collect Flow into List
46. @Test fun `should get users`() = runBlockingTest { val usersList = usersRepository.getUsers().toList() assertEquals(usersList, listOf("User 2", "User 5")) } Assert on returned user names
47. @Test fun `should get users`() = runBlockingTest { val usersList = usersRepository.getUsers().toList() assertEquals(users, listOf("User 2", "User 5")) } Is there a better way to collect from Flows in test?
48. cashApp/turbine Code ! Issues Pull Requests Turbine Small testing library for kotlinx.coroutines Flow. testImplementation 'app.cash.turbine:turbine:0.2.1'
49. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } Library has test extension on Flow
50. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } Read from item from Flow
51. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } Assertion
52. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } Use expectItem to fetch each item
53. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } Verify no more emission by Flow
54. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } What if flow emitted more items than 2?
55. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } UserRepoTests.kt Run: UserRepoTest should get users app.cash.turbine.AssertionError: Expected complete but found Item(User 6) One more item in Flow
56. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectItem() shouldBe "User 6” expectComplete() } } UserRepoTests.kt Run: UserRepoTest should get users Add expect item
57. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } What if we didn’t expect complete?
58. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" } } UserRepoTests.kt Run: UserRepoTest should get users app.cash.turbine.AssertionError: Unconsumed events found: - Complete Need to assert flow finished
59. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } UserRepoTests.kt Run: should get users UserRepoTest
60. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } UserRepoTests.kt Run: should get users UserRepoTest How does this work?
61. Flow to test How Turbine Works
62. Channel (Unlimited) How Turbine Works
63. Channel (Unlimited) sealed class Event<out T> { object Complete data class Error(""...) data class Item(val value: T) } Event How Turbine Works
64. Channel (Unlimited) data class Item(val value: T): Event() How Turbine Works
65. Channel (Unlimited) data class Item(val value: T): Event() How Turbine Works
66. Channel (Unlimited) data class Item(val value: T): Event() How Turbine Works
67. Channel (Unlimited) object Complete: Event() How Turbine Works
68. Channel (Unlimited) Exception data class Error(""...): Event() How Turbine Works
69. Channel (Unlimited) How do I query items in channels? How Turbine Works
70. interface FlowTurbine<T> { val timeout: Duration fun expectNoEvents() suspend fun expectItem(): T fun expectError(): Throwable suspend fun expectComplete() } API to verify emissions How Turbine Works
71. interface FlowTurbine<T> { val timeout: Duration fun expectNoEvents() suspend fun expectItem(): T fun expectError(): Throwable suspend fun expectComplete() } Verify duration of emission How Turbine Works
72. interface FlowTurbine<T> { val timeout: Duration fun expectNoEvents() suspend fun expectItem(): T fun expectError(): Throwable suspend fun expectComplete() } Verify no emissions How Turbine Works
73. interface FlowTurbine<T> { val timeout: Duration fun expectNoEvents() suspend fun expectItem(): T fun expectError(): Throwable suspend fun expectComplete() } Verify item emitted How Turbine Works
74. interface FlowTurbine<T> { val timeout: Duration fun expectNoEvents() suspend fun expectItem(): T fun expectError(): Throwable suspend fun expectComplete() } Verify error occurred How Turbine Works
75. interface FlowTurbine<T> { val timeout: Duration fun expectNoEvents() suspend fun expectItem(): T fun expectError(): Throwable suspend fun expectComplete() } Verify all items emitted How Turbine Works
76. interface FlowTurbine<T> { val timeout: Duration fun expectNoEvents() suspend fun expectItem(): T fun expectError(): Throwable suspend fun expectComplete() } How Turbine Works
77. How Turbine Works suspend fun <T> Flow<T>.test(""...) { coroutineScope { } Create a coroutine
78. How Turbine Works suspend fun <T> Flow<T>.test(""...) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) } Channel of events
79. How Turbine Works suspend fun <T> Flow<T>.test(""...) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) launch { } }
80. How Turbine Works suspend fun <T> Flow<T>.test(""...) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) launch { collect { item "-> events.send(Event.Item(item)) } } Store emissions
81. How Turbine Works suspend fun <T> Flow<T>.test(""...) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) launch { try { collect { ""... } } catch { events.send(Event.Error) } } Send error to Channel
82. How Turbine Works suspend fun <T> Flow<T>.test( validate: suspend FlowTurbine<T>.() "-> Unit ) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) launch { try { collect { ""... } } catch { events.send(Event.Error) Lambda block
83. How Turbine Works suspend fun <T> Flow<T>.test( validate: suspend FlowTurbine<T>.() "-> Unit ) { coroutineScope { val events = Channel<Event<T">>(UNLIMITED) launch { try { collect { ""... } } catch { events.send(Event.Error) API
84. @Test fun `should get users`() = runBlockingTest { val users = usersRepository.getUsers().test { expectItem() shouldBe "User 2" expectItem() shouldBe "User 5" expectComplete() } } Read emissions with API
85. Flow Test Cases • Collection • Run on Dispatcher • Errors • Retries Fail • Retry Succeeds
86. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } Run on Dispatcher
87. class UsersRepository( val apiService: ApiService, val dispatcher: CoroutineDispatcher ) { fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) } Inject Dispatcher
88. class UsersRepository( val apiService: ApiService, val dispatcher: CoroutineDispatcher ) { fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .flowOn(dispatcher) } Use Dispatcher
89. class UsersRepository( val apiService: ApiService, val dispatcher: CoroutineDispatcher ) { fun getUsers(): Result<String> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .flowOn(dispatcher) }
90. @Test fun `should get users`() = runBlockingTest { usersRepository.getUsers().test { expectError() } } How do I use a custom dispatcher?
91. @Test fun `should get users`() = runBlockingTest { usersRepository.getUsers().test { expectError() } } fun TestCoroutineDispatcher.runBlockingTest(""...)
92. val dispatcher = TestCoroutineDispatcher() val usersRepository = UsersRepository(""..., dispatcher) @Test fun `should get users`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { expectError() } }
93. val dispatcher = TestCoroutineDispatcher() val usersRepository = UsersRepository(""..., dispatcher) @Test fun `should get users`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { expectError() } }
94. val dispatcher = TestCoroutineDispatcher() val usersRepository = UsersRepository(""..., dispatcher) @Test fun `should get users`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { expectError() } }
95. Flow Test Cases • Collection • Run on Dispatcher • Errors • Retries Fail • Retry Succeeds
96. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> { return apiService.getUsers() .filter { it.location "== "NYC" } .map { it.name } } } Test Error?
97. @Test fun `should handle error`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { expectError() } }
98. @Test fun `should handle error`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) usersRepository.getUsers().test { expectError() } } Mock API method
99. @Test fun `should handle error`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw Exception() } usersRepository.getUsers().test { expectError() } } Throw exception
100. @Test fun `should handle error`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw Exception() } usersRepository.getUsers().test { expectError() } } Verify error is thrown
101. @Test fun `should handle error`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw Exception() } usersRepository.getUsers().test { expectError() } } UserRepoTests.kt Run: should handle error UserRepoTest
102. @Test fun `should handle error`() = runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw Exception() } usersRepository.getUsers().test { expectError() } } UserRepoTests.kt Run: should handle error UserRepoTest Try Catch
103. class UsersRepository(val apiService: ApiService) { fun getUsers(): Flow<String> = apiService.getUsers() .filter { it.location "== "NYC" } .map { it.name } } Better way to handle errors?
104. inline class Result { fun <T> success(value: T) fun <T> failure(exception: Throwable) } Union to represent success or failure
105. fun getUsers(): Flow<Result<String">> = return apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .catch { emit(Result.failure(it)) } Flow emits Results
106. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .catch { emit(Result.failure(it)) } Success
107. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .catch { emit(Result.failure(it)) } Emit Result Failure
108. @Test fun `should handle error`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw Exception() } usersRepository.getUsers().test { } }
109. @Test fun `should handle error`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw Exception() } usersRepository.getUsers().test { expectItem().isFailure.shouldBeTrue() expectComplete() } } Verify Result is failure
110. @Test fun `should handle error`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw Exception() } usersRepository.getUsers().test { expectItem().isFailure expectComplete() } } Verify no more emissions
111. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .catch { emit(Result.failure(it)) } Exception
112. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .catch { emit(Result.failure(it)) } Emit Result item
113. Flow Test Cases • Collection • Run on Dispatcher • Errors • Retries Fail • Retry Succeeds
114. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Exception
115. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Catch Exception
116. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Retry?
117. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Retry 2-times
118. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Delay for each retry
119. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Error
120. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Retry
121. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Delay 2 seconds
122. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Try running Flow again
123. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Retry fails, go to catch
124. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher)
125. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) How do we test retries?
126. @Test fun `should retry twice`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { advanceTimeBy(2000) advanceTimeBy(2000) expectItem().isFailure.shouldBeTrue() expectComplete() } }
127. @Test fun `should retry twice`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw IOException() } usersRepository.getUsers().test { advanceTimeBy(2000) advanceTimeBy(2000) expectItem().isFailure.shouldBeTrue() expectComplete() } } Throw Exception
128. @Test fun `should retry twice`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw IOException() } usersRepository.getUsers().test { expectItem().isFailure.shouldBeTrue() expectComplete() } } Read from Flow
129. @Test fun `should retry twice`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw IOException() } usersRepository.getUsers().test { expectItem().isFailure.shouldBeTrue() expectComplete() } } Verify Result is Failure
130. @Test fun `should retry twice`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw IOException() } usersRepository.getUsers().test { expectItem().isFailure.shouldBeTrue() expectComplete() } }
131. @Test fun `should retry twice`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw IOException() } usersRepository.getUsers().test { expectItem().isFailure.shouldBeTrue() expectComplete() } } UserRepoTests.kt Run: UserRepoTest should retry twice kotlinx.coroutines.TimeoutCancellationException: Timed out waiting for 1000 ms ! ! Timeout Exception
132. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Error
133. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Retry
134. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Delay 2 seconds
135. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Advance virtual time forward
136. @Test fun `should retry twice`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw IOException() } usersRepository.getUsers().test { advanceTimeBy(2000) expectItem().isFailure.shouldBeTrue() expectComplete() } } Advance virtual time on dispatcher
137. @Test fun `should retry twice`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw IOException() } usersRepository.getUsers().test { advanceTimeBy(2000) expectItem().isFailure.shouldBeTrue() expectComplete() } } Advance time by 2 seconds
138. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Retry
139. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Delay for before 2nd retry
140. @Test fun `should retry twice`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw IOException() } usersRepository.getUsers().test { advanceTimeBy(2000) advanceTimeBy(2000) expectItem().isFailure.shouldBeTrue() expectComplete() } } Advance time forward for 2nd retry
141. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) 2nd Retry
142. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) All Retries failed
143. @Test fun `should retry twice`() = dispatcher.runBlockingTest { whenever(apiService.getUsers()) doReturn flow { throw IOException() } usersRepository.getUsers().test { advanceTimeBy(2000) advanceTimeBy(2000) expectItem().isFailure.shouldBeTrue() expectComplete() } }
144. Flow Test Cases • Collection • Run on Dispatcher • Errors • Retries Fail • Retry Succeeds
145. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) 2nd Retry Succeeds
146. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Apply Filter, Map
147. var throwError = false whenever(apiService.getUsers()) doReturn flow { if (throwError) { throw IOException() } else { emit(User(1, "User 1", "NYC")) } } Flag to control sending error
148. var throwError = false whenever(apiService.getUsers()) doReturn flow { if (throwError) { throw IOException() } else { emit(User(1, "User 1", "NYC")) } } Mock API Service to return Flow
149. var throwError = false whenever(apiService.getUsers()) doReturn flow { if (throwError) { throw IOException() } else { emit(User(1, "User 1", "NYC")) } } Throw Error on exception
150. var throwError = false whenever(apiService.getUsers()) doReturn flow { if (throwError) { throw IOException() } else { emit(User(1, "User 1", "NYC")) } } Emit User
151. @Test fun `should retry succeed`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { advanceTimeBy(2000) throwError = false advanceTimeBy(2000) expectItem().isSuccess.shouldBeTrue() expectComplete() } } Retry
152. @Test fun `should retry succeed`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { advanceTimeBy(2000) throwError = false advanceTimeBy(2000) expectItem().isSuccess.shouldBeTrue() expectComplete() } } Flow will return data
153. @Test fun `should retry succeed`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { advanceTimeBy(2000) throwError = false advanceTimeBy(2000) expectItem().isSuccess.shouldBeTrue() expectComplete() } } 2nd Retry
154. @Test fun `should retry succeed`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { advanceTimeBy(2000) throwError = false advanceTimeBy(2000) expectItem().isSuccess.shouldBeTrue() expectComplete() } } Verify Success
155. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) 2nd Retry
156. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher)
157. fun getUsers(): Flow<Result<String">> = apiService.getUsers() .filter { it.location "== "NYC" } .map { Result.success(it.name) } .retry(2) { delay(2000) true } .catch { emit(Result.failure(it)) } .flowOn(dispatcher) Operators
158. @Test fun `should retry succeed`() = dispatcher.runBlockingTest { usersRepository.getUsers().test { advanceTimeBy(2000) throwError = false advanceTimeBy(2000) expectItem().isSuccess.shouldBeTrue() expectComplete() } }
159. Flow Test Cases • Collection • Run on Dispatcher • Errors • Retries Fail • Retry Succeeds
160. View Model Testing
161. Flow of users Repository Service
162. View Model Repository
163. class UserViewModel(): ViewModel() { val states = MutableStateFlow(State()) fun getData() { usersRepository.getUsers() .onEach { states.value = State(data = it.get()) } .launchIn(viewModelScope) } } data class State(val data: String = "") Jetpack View Model
164. class UserViewModel(val usersRepository: UsersRepository): ViewModel() { val states = MutableStateFlow(State()) fun getData() { usersRepository.getUsers() .onEach { states.value = State(data = it.get()) } .launchIn(viewModelScope) } } data class State(val data: String = "") Inject Repo
165. class UserViewModel(val usersRepository: UsersRepository): ViewModel() { val states = MutableStateFlow("") fun getData() { usersRepository.getUsers() .onEach { states.value = State(data = it.get()) } .launchIn(viewModelScope) } } State Flow
166. class UserViewModel(val usersRepository: UsersRepository): ViewModel() { val states = MutableStateFlow("") fun getData() { usersRepository.getUsers() .onEach { states.value = State(data = it.get()) } .launchIn(viewModelScope) } } Flow of user names
167. class UserViewModel(val usersRepository: UsersRepository): ViewModel() { val states = MutableStateFlow("") fun getData() { usersRepository.getUsers() .onEach { states.value = it } .launchIn(viewModelScope) } } Update State flow for each emission
168. class UserViewModel(val usersRepository: UsersRepository): ViewModel() { val states = MutableStateFlow("") fun getData() { usersRepository.getUsers() .onEach { states.value = it } .launchIn(viewModelScope) } } Launch coroutine in view module sopce
169. class UserViewModel(val usersRepository: UsersRepository): ViewModel() { val states = MutableStateFlow("") fun getData() { usersRepository.getUsers() .onEach { states.value = it } .launchIn(viewModelScope) } }
170. val repo = mock<UsersRepository>() val viewModel = UserViewModel(repo) Inject mock into view model
171. @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf(Result.success("User")) viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User" } }
172. @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf(Result.success("User")) viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User" } } Mock flow
173. @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf("User") viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User" } } Emit Successful response
174. @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf("User") viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User" } } Run test
175. @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf("User") viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User" } } Verify emission
176. @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf(Result.success("User")) viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User" } } ViewModelTest.kt Run: ViewModelTest should get data Module with the Main dispatcher had failed to initialize. For tests Dispatchers.setMain from kotlinx-coroutines-test module can be used
177. val dispatcher = TestCoroutineDispatcher() @Before fun setUp() { Dispatchers.setMain(dispatcher) } @After fun tearDown() { Dispatchers.resetMain() } Set Main Dispatcher
178. val dispatcher = TestCoroutineDispatcher() @Before fun setUp() { Dispatchers.setMain(dispatcher) } @After fun tearDown() { Dispatchers.resetMain() } Reset Main Dispatcher
179. class CoroutineTestRule(testDispatcher) : TestWatcher() { override fun starting(description) { Dispatchers.setMain(testDispatcher) } override fun finished(description) { Dispatchers.resetMain() testDispatcher.cleanupTestCoroutines() } }
180. class CoroutineTestRule(testDispatcher) : TestWatcher() { override fun starting(description) { Dispatchers.setMain(testDispatcher) } override fun finished(description) { Dispatchers.resetMain() testDispatcher.cleanupTestCoroutines() } }
181. class CoroutineTestRule(testDispatcher) : TestWatcher() { override fun starting(description) { Dispatchers.setMain(testDispatcher) } override fun finished(description) { Dispatchers.resetMain() testDispatcher.cleanupTestCoroutines() } }
182. @get:Rule var testRule = CoroutineTestRule() @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf("User") viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User" } }
183. @get:Rule var testRule = CoroutineTestRule() @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf(Result.success("User")) viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User" } } ViewModelTest.kt Run: ViewModelTest should get data
184. @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf( "User 1", "User 2" ) viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User 1" expectItem().data shouldBe "User 2" expectComplete() } Return 2 results
185. @Test fun `should get data`() = runBlockingTest { whenever(repo.getUsers()) doReturn flowOf( "User 1", "User 2" ) viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User 1" expectItem().data shouldBe "User 2" expectComplete() } Return 2 results
186. @Test fun `should get data`() = runBlockingTest { viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User 1" expectItem().data shouldBe "User 2" expectComplete() } Verification
187. @Test fun `should get data`() = runBlockingTest { viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User 1" expectItem().data shouldBe "User 2" expectComplete() } ViewModelTest.kt Run: ViewModelTest should get data java.lang.AssertionError: Expected <User 1>, actual <User 2> are not the same instance.
188. @Test fun `should get data`() = runBlockingTest { viewModel.getData() viewModel.states.test { expectItem().data shouldBe "User 1" expectItem().data shouldBe "User 2" expectComplete() } ViewModelTest.kt Run: ViewModelTest should get data java.lang.AssertionError: Expected <User 1>, actual <User 2> are not the same instance. Assertion failed
189. class UserViewModel(val usersRepository: UsersRepository): ViewModel() { val states = MutableStateFlow(State()) fun getData() { usersRepository.getUsers() .onEach { states.value = State(it) } .launchIn(viewModelScope) } } Conflated
190. Channels • Broadcast Channel • Unlimited Channel • Buffered Channel • Mutable Shared Flow
191. class UserViewModel(val usersRepository: UsersRepository): ViewModel() { val sharedFlow = MutableSharedFlow<String>() }
192. class UserViewModel(val usersRepository: UsersRepository): ViewModel() { val sharedFlow = MutableSharedFlow<String>() fun getData() { usersRepository.getUsers() .onEach { states.emit(it) } .launchIn(viewModelScope) } }
193. Channels • Broadcast Channel • Unlimited Channel • Buffered Channel • Mutable Shared Flow
194. https:"//codingwithmohit.com/coroutines/unit-testing-delays-errors-retries-with-kotlin-flows/ Unit Testing
195. Resources • Unit Testing Delays, Errors & Retries with Kotlin Flows https:"//codingwithmohit.com/coroutines/unit-testing-delays- errors-retries-with-kotlin-flows/ • Unit Testing Channels & Flows in Practice https:"//www.youtube.com/watch?v=h8bLIUi6HWU
196. Thank You! www.twitter.com/heyitsmohit www.codingwithmohit.com