Untangling Coroutine Testing (Droidcon Berlin 2022)

Coroutines are embraced on Android as a tool to perform asynchronous operations and manage threading in your apps. Testing them requires some extra work and a solid understanding of scopes and dispatchers. In this talk, we’ll look at how to test coroutines with the latest available testing APIs introduced in kotlinx.coroutines 1.6, from the simplest cases all the way to Flows.

For more, see
https://zsmb.co/talks/untangling-coroutine-testing/

Transcript

1. Untangling Coroutine Testing Márton Braun @zsmb13 Developer Relations Engineer Google
2. Agenda • Testing suspending functions • The coroutine test APIs • Best practices • Handling the Main dispatcher • Flows & StateFlows
3. Introduction What’s up with testing coroutines anyway?
4. Introduction
5. Introduction
6. kotlinx.coroutines.test Pre-1.6 APIs 1.6+ APIs
7. kotlinx.coroutines.test Pre-1.6 APIs runBlockingTest TestCoroutineDispatcher TestCoroutineScope pauseDispatcher resumeDispatcher 1.6+ APIs
8. kotlinx.coroutines.test 1.6+ APIs runTest TestDispatcher TestScope TestCoroutineScheduler Pre-1.6 APIs runBlockingTest TestCoroutineDispatcher TestCoroutineScope pauseDispatcher resumeDispatcher
9. kotlinx.coroutines.test 1.6+ APIs runTest TestDispatcher TestScope TestCoroutineScheduler Pre-1.6 APIs runBlockingTest TestCoroutineDispatcher TestCoroutineScope pauseDispatcher resumeDispatcher @Experimental
10. kotlinx.coroutines.test 1.6+ APIs runTest TestDispatcher TestScope TestCoroutineScheduler Pre-1.6 APIs runBlockingTest TestCoroutineDispatcher TestCoroutineScope pauseDispatcher resumeDispatcher @Experimental @Deprecated
11. kotlinx.coroutines.test 1.6+ APIs runTest TestDispatcher TestScope TestCoroutineScheduler Pre-1.6 APIs runBlockingTest TestCoroutineDispatcher TestCoroutineScope pauseDispatcher resumeDispatcher @Experimental @Deprecated @Experimental
12. kotlinx.coroutines.test goo.gle/coroutine-16-migration
13. Testing suspending functions runTest. run.
14. Testing suspending functions suspend fun fetchData(): String { delay(1000L) return "Hello world" }
15. Testing suspending functions suspend fun fetchData(): String { delay(1000L) return "Hello world" } @Test fun dataIsHelloWorld() { val data = fetchData() assertEquals("Hello world", data) }
16. Testing suspending functions suspend fun fetchData(): String { delay(1000L) return "Hello world" } @Test fun dataIsHelloWorld() { val data = fetchData() assertEquals("Hello world", data) }
17. Testing suspending functions suspend fun fetchData(): String { delay(1000L) return "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } import kotlinx.coroutines.test.runTest
18. Testing suspending functions suspend fun fetchData(): String { delay(1000L) return "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } import kotlinx.coroutines.test.runTest
19. Testing suspending functions suspend fun fetchData(): String { delay(1000L) return "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } import kotlinx.coroutines.test.runTest
20. Testing suspending functions suspend fun fetchData(): String { delay(1000L) return "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } import kotlinx.coroutines.test.runTest
21. Testing suspending functions suspend fun fetchData(): String { delay(1000L) return "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } import kotlinx.coroutines.test.runTest
22. Testing Dispatcher changes suspend fun fetchData(): String = withContext(Dispatchers.IO) { delay(1000L) "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } import kotlinx.coroutines.test.runTest
23. Testing Dispatcher changes suspend fun fetchData(): String = withContext(Dispatchers.IO) { delay(1000L) "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } import kotlinx.coroutines.test.runTest *
24. Testing Dispatcher changes suspend fun fetchData(): String = withContext(Dispatchers.IO) { delay(1000L) "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } Test thread Dispatchers.IO
25. Testing Dispatcher changes suspend fun fetchData(): String = withContext(Dispatchers.IO) { delay(1000L) "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } Test thread Dispatchers.IO fetchData()
26. Testing Dispatcher changes suspend fun fetchData(): String = withContext(Dispatchers.IO) { delay(1000L) "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } Test thread Dispatchers.IO fetchData()
27. Testing Dispatcher changes suspend fun fetchData(): String = withContext(Dispatchers.IO) { delay(1000L) "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } Test thread Dispatchers.IO fetchData() delay()
28. Testing Dispatcher changes suspend fun fetchData(): String = withContext(Dispatchers.IO) { delay(1000L) "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } Test thread Dispatchers.IO fetchData() delay()
29. Testing Dispatcher changes suspend fun fetchData(): String = withContext(Dispatchers.IO) { delay(1000L) "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } Test thread Dispatchers.IO fetchData() delay() assert()
30. Testing Dispatcher changes suspend fun fetchData(): String = withContext(Dispatchers.IO) { delay(1000L) "Hello world" } @Test fun dataIsHelloWorld() = runTest { val data = fetchData() assertEquals("Hello world", data) } Test thread Dispatchers.IO fetchData() delay() assert()
31. Testing new coroutines
32. Testing new coroutines @Test fun directExample() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals( listOf("Alice", "Bob"), repo.getAllUsers() ) }
33. Testing new coroutines @Test fun directExample() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals( listOf("Alice", "Bob"), repo.getAllUsers() ) }
34. Testing new coroutines class ProfileViewModel : ViewModel() { lateinit var user: User fun initialize() { viewModelScope.launch { user = fetchUser() } } } @Test fun directExample() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals( listOf("Alice", "Bob"), repo.getAllUsers() ) }
35. Testing new coroutines class ProfileViewModel : ViewModel() { lateinit var user: User fun initialize() { viewModelScope.launch { user = fetchUser() } } } @Test fun indirectExample() = runTest { val viewModel = ProfileViewModel() viewModel.initialize() assertEquals("Sam", viewModel.user.name) } @Test fun directExample() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals( listOf("Alice", "Bob"), repo.getAllUsers() ) }
36. Testing new coroutines class ProfileViewModel : ViewModel() { lateinit var user: User fun initialize() { viewModelScope.launch { user = fetchUser() } } } @Test fun indirectExample() = runTest { val viewModel = ProfileViewModel() viewModel.initialize() assertEquals("Sam", viewModel.user.name) } @Test fun directExample() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals( listOf("Alice", "Bob"), repo.getAllUsers() ) }
37. Testing new coroutines class ProfileViewModel : ViewModel() { lateinit var user: User fun initialize() { viewModelScope.launch { user = fetchUser() } } } @Test fun indirectExample() = runTest { val viewModel = ProfileViewModel() viewModel.initialize() assertEquals("Sam", viewModel.user.name) } @Test fun directExample() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals( listOf("Alice", "Bob"), repo.getAllUsers() ) }
38. The coroutine test APIs The latest and greatest in kotlinx.coroutines.test
39. Test APIs runTest
40. Test APIs runTest TestScope
41. Test APIs runTest TestDispatcher TestScope
42. Test APIs runTest TestDispatcher TestCoroutineScheduler TestScope
43. Test APIs runTest TestDispatcher TestCoroutineScheduler TestScope TestDispatcher TestDispatcher
44. Test APIs runTest TestCoroutineScheduler TestScope TestDispatcher TestDispatcher All TestDispatchers must share the same scheduler TestDispatcher
45. Test APIs TestDispatcher TestCoroutineScheduler
46. Test APIs TestCoroutineScheduler StandardTestDispatcher UnconfinedTestDispatcher TestDispatcher
47. StandardTestDispatcher
48. • Queues up coroutines on the scheduler StandardTestDispatcher
49. • Queues up coroutines on the scheduler • You need to advance those coroutines manually StandardTestDispatcher
50. • Queues up coroutines on the scheduler • You need to advance those coroutines manually • runTest uses a StandardTestDispatcher by default StandardTestDispatcher runTest StandardTestDispatcher TestScope
51. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) }
52. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } this: TestScope
53. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) }
54. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo()
55. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() reg("Alice")
56. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() reg("Bob") reg("Alice")
57. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() assert() reg("Bob") reg("Alice")
58. StandardTestDispatcher UserRepo() assert() @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } reg("Bob") reg("Alice")
59. • You need to advance those coroutines manually StandardTestDispatcher
60. • You need to advance those coroutines manually StandardTestDispatcher 80 ms 90 ms 100 ms 500 ms 750 ms
61. • You need to advance those coroutines manually StandardTestDispatcher • runCurrent() 80 ms 90 ms 100 ms 500 ms 750 ms
62. • You need to advance those coroutines manually StandardTestDispatcher • runCurrent() 80 ms 90 ms 100 ms 500 ms 750 ms
63. • You need to advance those coroutines manually StandardTestDispatcher • runCurrent() • advanceTimeBy(delayTimeMillis: Long) 80 ms 90 ms 100 ms 500 ms 750 ms
64. • You need to advance those coroutines manually StandardTestDispatcher 80 ms 90 ms 100 ms 500 ms 750 ms • runCurrent() • advanceTimeBy(delayTimeMillis = 100)
65. • You need to advance those coroutines manually StandardTestDispatcher • runCurrent() • advanceTimeBy(delayTimeMillis = 100) 80 ms 90 ms 100 ms 500 ms 750 ms
66. • You need to advance those coroutines manually StandardTestDispatcher • runCurrent() • advanceTimeBy(delayTimeMillis: Long) • advanceUntilIdle() 80 ms 90 ms 100 ms 500 ms 750 ms
67. • You need to advance those coroutines manually StandardTestDispatcher • runCurrent() • advanceTimeBy(delayTimeMillis: Long) • advanceUntilIdle() 80 ms 90 ms 100 ms 500 ms 750 ms
68. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) }
69. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) }
70. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) }
71. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo()
72. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() reg("Alice")
73. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() reg("Bob") reg("Alice")
74. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() reg("Alice") reg("Bob")
75. Idle StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() reg("Alice") reg("Bob")
76. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() reg("Alice") reg("Bob") Idle
77. StandardTestDispatcher UserRepo() reg("Alice") reg("Bob") @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) }
78. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() reg("Alice") reg("Bob") assert()
79. StandardTestDispatcher @Test fun standardTest() = runTest { val repo = UserRepository() launch { repo.register("Alice") } launch { repo.register("Bob") } advanceUntilIdle() assertEquals(listOf("Alice", "Bob"), repo.getAllUsers()) } UserRepo() reg("Alice") reg("Bob") assert()
80. UnconfinedTestDispatcher
81. UnconfinedTestDispatcher • Starts new coroutines eagerly (like runBlockingTest)
82. UnconfinedTestDispatcher • Starts new coroutines eagerly (like runBlockingTest) • Can be a good choice for simple tests
83. UnconfinedTestDispatcher • Starts new coroutines eagerly (like runBlockingTest) • Can be a good choice for simple tests • Does not emulate real concurrency
84. UnconfinedTestDispatcher @Test fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) { val userRepo = UserRepository() launch { userRepo.register("Alice") } launch { userRepo.register("Bob") } assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers()) }
85. UnconfinedTestDispatcher @Test fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) { val userRepo = UserRepository() launch { userRepo.register("Alice") } launch { userRepo.register("Bob") } assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers()) }
86. UnconfinedTestDispatcher @Test fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) { val userRepo = UserRepository() launch { userRepo.register("Alice") } launch { userRepo.register("Bob") } assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers()) } this: TestScope
87. UnconfinedTestDispatcher @Test fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) { val userRepo = UserRepository() launch { userRepo.register("Alice") } launch { userRepo.register("Bob") } assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers()) } UserRepo()
88. UnconfinedTestDispatcher @Test fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) { val userRepo = UserRepository() launch { userRepo.register("Alice") } launch { userRepo.register("Bob") } assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers()) } UserRepo() reg("Alice")
89. UnconfinedTestDispatcher @Test fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) { val userRepo = UserRepository() launch { userRepo.register("Alice") } launch { userRepo.register("Bob") } assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers()) } UserRepo() reg("Alice") reg("Bob")
90. UnconfinedTestDispatcher @Test fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) { val userRepo = UserRepository() launch { userRepo.register("Alice") } launch { userRepo.register("Bob") } assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers()) } UserRepo() reg("Alice") reg("Bob") assert()
91. UnconfinedTestDispatcher @Test fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) { val userRepo = UserRepository() launch { userRepo.register("Alice") } launch { userRepo.register("Bob") } assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers()) } UserRepo() reg("Alice") reg("Bob") assert()
92. TestDispatchers StandardTestDispatcher Queues up new coroutines Use by default UnconfinedTestDispatcher Starts new coroutines eagerly Use selectively
93. TestDispatchers Queues up new coroutines Use by default Starts new coroutines eagerly Use selectively • While migrating tests from old APIs • As the Main dispatcher • For coroutines that collect values StandardTestDispatcher UnconfinedTestDispatcher
94. Injecting dispatchers Something something heat exchangers
95. Injecting dispatchers class Repository(private val database: Database) { private val scope = CoroutineScope(Dispatchers.IO) fun initialize() { scope.launch { database.populate() } } suspend fun fetchData(): String = withContext(Dispatchers.IO) { database.read() } }
96. Injecting dispatchers class Repository(private val database: Database) { private val scope = CoroutineScope(Dispatchers.IO) fun initialize() { scope.launch { database.populate() } } suspend fun fetchData(): String = withContext(Dispatchers.IO) { database.read() } }
97. Injecting dispatchers class Repository(private val database: Database) { private val scope = CoroutineScope(Dispatchers.IO) fun initialize() { scope.launch { database.populate() } } suspend fun fetchData(): String = withContext(Dispatchers.IO) { database.read() } }
98. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository(FakeDatabase()) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) }
99. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository(FakeDatabase()) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) } Test thread Dispatchers.IO
100. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository(FakeDatabase()) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(FakeDb()) Test thread Dispatchers.IO
101. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository(FakeDatabase()) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(FakeDb()) Test thread Dispatchers.IO db.populate() fun initialize() { scope.launch { database.populate() } }
102. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository(FakeDatabase()) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(FakeDb()) Test thread Dispatchers.IO db.read() db.populate() suspend fun fetchData() = withContext(Dispatchers.IO) { database.read() }
103. assert() Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository(FakeDatabase()) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(FakeDb()) Test thread Dispatchers.IO db.read() db.populate()
104. assert() Injecting dispatchers Repo(FakeDb()) Test thread Dispatchers.IO db.read() db.populate() @Test fun repoTest() = runTest { val repository = Repository(FakeDatabase()) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) }
105. Injecting dispatchers Repo(FakeDb()) Test thread Dispatchers.IO db.read() db.populate() assert() @Test fun repoTest() = runTest { val repository = Repository(FakeDatabase()) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) }
106. Injecting dispatchers Repo(FakeDb()) Test thread Dispatchers.IO db.read() db.populate() assert() @Test fun repoTest() = runTest { val repository = Repository(FakeDatabase()) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) }
107. , ioDispatcher ioDispatcher Injecting dispatchers class Repository( Dispatchers.IO) fun initialize() { scope.launch { database.populate() } } suspend fun fetchData(): String = withContext( ) { database.read() } } private val database: Database) { private val scope = CoroutineScope( Dispatchers.IO
108. Dispatchers.IO Injecting dispatchers class Repository( private val ioDispatcher: CoroutineDispatcher = Dispatchers.IO, ioDispatcher) fun initialize() { scope.launch { database.populate() } } suspend fun fetchData(): String = withContext( ) { database.read() } } private val database: Database ) { private val scope = CoroutineScope( ioDispatcher ,
109. Dispatchers.IO Injecting dispatchers class Repository( private val ioDispatcher: CoroutineDispatcher = Dispatchers.IO, ioDispatcher) fun initialize() { scope.launch { database.populate() } } suspend fun fetchData(): String = withContext( ) { database.read() } } private val database: Database ) { private val scope = CoroutineScope( ioDispatcher ,
110. FakeDatabase(), @Test fun repoTest() = runTest { val repository = Repository( ) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) } Injecting dispatchers
111. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = , ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } FakeDatabase()
112. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } this: TestScope
113. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) }
114. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(...)
115. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } fun initialize() { scope.launch { database.populate() } } Repo(...)
116. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(...) db.populate() fun initialize() { scope.launch { database.populate() } }
117. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(...) db.populate()
118. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(...) db.populate()
119. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(...) db.populate() db.read() suspend fun fetchData() = withContext(ioDispatcher) { database.read() }
120. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } Repo(...) db.populate() db.read() assert()
121. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() advanceUntilIdle() val data = repository.fetchData() assertEquals("Hello world", data) } fun initialize() { scope.launch { database.populate() } } This is a bad API, don’t do this
122. Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize().await(). val data = repository.fetchData() assertEquals("Hello world", data) } fun initialize(): Deferred<Unit> { return scope.async { } } database.populate()
123. suspend fun initialize() { } Injecting dispatchers @Test fun repoTest() = runTest { val repository = Repository( database = FakeDatabase(), ioDispatcher = StandardTestDispatcher(testScheduler), ) repository.initialize() val data = repository.fetchData() assertEquals("Hello world", data) } database.populate()
124. Handling the Main dispatcher A UI thread without a UI
125. Handling the Main dispatcher class HomeViewModel : ViewModel() { private val _message = MutableStateFlow("") val message: StateFlow<String> get() = _message fun loadMessage() { viewModelScope.launch { _message.value = "Greetings!" } } }
126. Handling the Main dispatcher class HomeViewModel : ViewModel() { private val _message = MutableStateFlow("") val message: StateFlow<String> get() = _message fun loadMessage() { viewModelScope.launch { _message.value = "Greetings!" } } }
127. Handling the Main dispatcher } val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) @Test fun testGreeting() = runTest {
128. Handling the Main dispatcher } val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) @Test fun testGreeting() = runTest { java.lang.IllegalStateException: Module with the Main dispatcher had failed to initialize. For tests Dispatchers.setMain from kotlinx-coroutines-test module can be used
129. Handling the Main dispatcher } val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) @Test fun testGreeting() = runTest { java.lang.IllegalStateException: Module with the Main dispatcher had failed to initialize. For tests Dispatchers.setMain from kotlinx-coroutines-test module can be used
130. Handling the Main dispatcher val testDispatcher = UnconfinedTestDispatcher(testScheduler) Dispatchers.setMain(testDispatcher) val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) } @Test fun testGreeting() = runTest { java.lang.IllegalStateException: Module with the Main dispatcher had failed to initialize. For tests Dispatchers.setMain from kotlinx-coroutines-test module can be used
131. Handling the Main dispatcher val testDispatcher = UnconfinedTestDispatcher(testScheduler) Dispatchers.setMain(testDispatcher) val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) } @Test fun testGreeting() = runTest { java.lang.IllegalStateException: Module with the Main dispatcher had failed to initialize. For tests Dispatchers.setMain from kotlinx-coroutines-test module can be used
132. java.lang.IllegalStateException: Module with the Main dispatcher had failed to initialize. For tests Dispatchers.setMain from kotlinx-coroutines-test module can be used Handling the Main dispatcher val testDispatcher = UnconfinedTestDispatcher(testScheduler) Dispatchers.setMain(testDispatcher) try { } finally { Dispatchers.resetMain() } val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) } @Test fun testGreeting() = runTest {
133. Handling the Main dispatcher @Test fun testGreeting() = runTest { val testDispatcher = UnconfinedTestDispatcher(testScheduler) Dispatchers.setMain(testDispatcher) try { val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) } finally { Dispatchers.resetMain() } }
134. Handling the Main dispatcher @Test fun testGreeting() = runTest { val testDispatcher = UnconfinedTestDispatcher(testScheduler) Dispatchers.setMain(testDispatcher) try { val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) } finally { Dispatchers.resetMain() } } fun loadMessage() { viewModelScope.launch { _message.value = "Greetings!" } }
135. Handling the Main dispatcher @Test fun testGreeting() = runTest { val testDispatcher = UnconfinedTestDispatcher(testScheduler) try { val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) } finally { } } Dispatchers.setMain(testDispatcher) Dispatchers.resetMain()
136. Handling the Main dispatcher class MainDispatcherRule( val testDispatcher: TestDispatcher = UnconfinedTestDispatcher(), ) : TestWatcher() { override fun starting(description: Description) { } override fun finished(description: Description) { } } Dispatchers.setMain(testDispatcher) Dispatchers.resetMain()
137. Handling the Main dispatcher class HomeViewModelTestUsingRule { @get:Rule val mainDispatcherRule = MainDispatcherRule() @Test fun testGreeting() = runTest { val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) } }
138. class HomeViewModelTestUsingRule { @get:Rule val mainDispatcherRule = MainDispatcherRule() @Test fun testGreeting() = runTest { Handling the Main dispatcher val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) } }
139. Handling the Main dispatcher val viewModel = HomeViewModel() viewModel.loadMessage() assertEquals("Greetings!", viewModel.message.value) If you replace the Main dispatcher with a TestDispatcher, all new TestDispatchers will automatically share its scheduler class HomeViewModelTestUsingRule { @get:Rule val mainDispatcherRule = MainDispatcherRule() @Test fun testGreeting() = runTest { } }
140. Handling the Main dispatcher val unconfinedDispatcher = UnconfinedTestDispatcher() val standardDispatcher = StandardTestDispatcher() If you replace the Main dispatcher with a TestDispatcher, all new TestDispatchers will automatically share its scheduler class HomeViewModelTestUsingRule { @get:Rule val mainDispatcherRule = MainDispatcherRule() @Test fun testGreeting() = runTest { } }
141. Flows Suspenseful streams
142. Flows interface DataSource { fun counts(): Flow<Int> } class Repository(private val dataSource: DataSource) { fun scores(): Flow<Int> { return dataSource.counts().map { it * 10 } } }
143. Flows Test Repository Fake Data Source
144. Flows interface DataSource { fun counts(): Flow<Int> } class Repository(private val dataSource: DataSource) { fun scores(): Flow<Int> { return dataSource.counts().map { it * 10 } } }
145. Flows interface DataSource { fun counts(): Flow<Int> } class Repository(private val dataSource: DataSource) { fun scores(): Flow<Int> { return dataSource.counts().map { it * 10 } } } class ColdFakeDataSource : DataSource { override fun counts(): Flow<Int> { return flowOf(1, 2, 3, 4) } }
146. Flows @Test fun useTerminalOperators() = runTest { val repository = Repository(ColdFakeDataSource()) }
147. Flows @Test fun useTerminalOperators() = runTest { val repository = Repository(ColdFakeDataSource()) val first = repository.scores().first() assertEquals(10, first) }
148. Flows @Test fun useTerminalOperators() = runTest { val repository = Repository(ColdFakeDataSource()) val first = repository.scores().first() assertEquals(10, first) val values = repository.scores().toList() assertEquals(10, values[0]) assertEquals(20, values[1]) assertEquals(4, values.size) }
149. Flows @Test fun useTerminalOperators() = runTest { val repository = Repository(ColdFakeDataSource()) val first = repository.scores().first() assertEquals(10, first) val values = repository.scores().toList() assertEquals(10, values[0]) assertEquals(20, values[1]) assertEquals(4, values.size) val someValues = repository.scores().take(2).toList() assertEquals(10, someValues[0]) assertEquals(20, someValues[1]) }
150. Flows class HotFakeDataSource : DataSource { private val flow = MutableSharedFlow<Int>() suspend fun emit(value: Int) = flow.emit(value) override fun counts(): Flow<Int> = flow }
151. Flows class HotFakeDataSource : DataSource { private val flow = MutableSharedFlow<Int>() suspend fun emit(value: Int) = flow.emit(value) override fun counts(): Flow<Int> = flow }
152. Flows class HotFakeDataSource : DataSource { private val flow = MutableSharedFlow<Int>() suspend fun emit(value: Int) = flow.emit(value) override fun counts(): Flow<Int> = flow }
153. Flows @Test fun continuouslyCollect() = runTest { val dataSource = HotFakeDataSource() val repository = Repository(dataSource) }
154. Flows @Test fun continuouslyCollect() = runTest { val dataSource = HotFakeDataSource() val repository = Repository(dataSource) val values = mutableListOf<Int>() }
155. Flows launch(UnconfinedTestDispatcher()) { collect { values += it } } @Test fun continuouslyCollect() = runTest { val dataSource = HotFakeDataSource() val repository = Repository(dataSource) val values = mutableListOf<Int>() } repository.scores().
156. Flows launch(UnconfinedTestDispatcher()) { toList(values) } repository.scores(). @Test fun continuouslyCollect() = runTest { val dataSource = HotFakeDataSource() val repository = Repository(dataSource) val values = mutableListOf<Int>() }
157. Flows launch(UnconfinedTestDispatcher()) { } } @Test fun continuouslyCollect() = runTest { val dataSource = HotFakeDataSource() val repository = Repository(dataSource) val values = mutableListOf<Int>() dataSource.emit(1) assertEquals(10, values[0]) repository.scores().toList(values) val collectJob =
158. Flows val collectJob = launch(UnconfinedTestDispatcher()) { } } collectJob.cancel() @Test fun continuouslyCollect() = runTest { val dataSource = HotFakeDataSource() val repository = Repository(dataSource) val values = mutableListOf<Int>() dataSource.emit(1) assertEquals(10, values[0]) repository.scores().toList(values)
159. Flows val collectJob = launch(UnconfinedTestDispatcher()) { repository.scores().toList(values) } dataSource.emit(1) assertEquals(10, values[0]) dataSource.emit(2) dataSource.emit(3) assertEquals(30, values.last()) assertEquals(3, values.size) } collectJob.cancel() @Test fun continuouslyCollect() = runTest { val dataSource = HotFakeDataSource() val repository = Repository(dataSource) val values = mutableListOf<Int>()
160. Flows with Turbine
161. StateFlows Look! It’s a stream! It’s a state holder!
162. Stream StateFlows State holder Source: Manuel Vivo
163. interface MyRepository { fun scores(): Flow<Int> } class MyViewModel(private val myRepository: MyRepository) : ViewModel() { private val _data = MutableStateFlow(0) val data: StateFlow<Int> = _data.asStateFlow() fun initialize() { viewModelScope.launch { myRepository.scores().collect { score -> _data.value = score } } } } StateFlows
164. interface MyRepository { fun scores(): Flow<Int> } class MyViewModel(private val myRepository: MyRepository) : ViewModel() { private val _data = MutableStateFlow(0) val data: StateFlow<Int> = _data.asStateFlow() fun initialize() { viewModelScope.launch { myRepository.scores().collect { score -> _data.value = score } } } } StateFlows
165. interface MyRepository { fun scores(): Flow<Int> } class MyViewModel(private val myRepository: MyRepository) : ViewModel() { private val _data = MutableStateFlow(0) val data: StateFlow<Int> = _data.asStateFlow() fun initialize() { viewModelScope.launch { myRepository.scores().collect { score -> _data.value = score } } } } StateFlows
166. interface MyRepository { fun scores(): Flow<Int> } class MyViewModel(private val myRepository: MyRepository) : ViewModel() { private val _data = MutableStateFlow(0) val data: StateFlow<Int> = _data.asStateFlow() fun initialize() { viewModelScope.launch { myRepository.scores().collect { score -> _data.value = score } } } } StateFlows
167. StateFlows Test ViewModel Fake Repository
168. StateFlows class HotFakeRepository : MyRepository { private val flow = MutableSharedFlow<Int>() suspend fun emit(value: Int) = flow.emit(value) override fun scores(): Flow<Int> = flow }
169. @get:Rule val mainDispatcherRule = MainDispatcherRule() StateFlows @Test fun testHotFakeRepository() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) }
170. StateFlows @Test fun testHotFakeRepository() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) }
171. StateFlows @Test fun testHotFakeRepository() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) assertEquals(0, viewModel.data.value) }
172. StateFlows @Test fun testHotFakeRepository() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) assertEquals(0, viewModel.data.value) viewModel.initialize() } fun initialize() { viewModelScope.launch { myRepository.scores().collect { score -> _data.value = score } } }
173. StateFlows @Test fun testHotFakeRepository() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) assertEquals(0, viewModel.data.value) viewModel.initialize() fakeRepository.emit(1) assertEquals(1, viewModel.data.value) }
174. StateFlows @Test fun testHotFakeRepository() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) assertEquals(0, viewModel.data.value) viewModel.initialize() fakeRepository.emit(1) assertEquals(1, viewModel.data.value) fakeRepository.emit(2) fakeRepository.emit(3) assertEquals(3, viewModel.data.value) }
175. StateFlows @Test fun testHotFakeRepository() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) assertEquals(0, viewModel.data.value) viewModel.initialize() fakeRepository.emit(1) assertEquals(1, viewModel.data.value) fakeRepository.emit(2) fakeRepository.emit(3) assertEquals(3, viewModel.data.value) }
176. StateFlows @Test fun testHotFakeRepository() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) assertEquals(0, viewModel.data.value) viewModel.initialize() fakeRepository.emit(1) assertEquals(1, viewModel.data.value) fakeRepository.emit(2) fakeRepository.emit(3) assertEquals(3, viewModel.data.value) }
177. StateFlows with stateIn private val _data = MutableStateFlow(0) _data.asStateFlow() fun initialize() { .launch { .collect { count -> _data.value = count } } } myRepository: MyRepository myRepository.scores() class MyViewModel( ) : ViewModel() { private val viewModelScope val data: StateFlow<Int> = }
178. StateFlows with stateIn myRepository: MyRepository myRepository.scores() .stateIn( , SharingStarted.WhileSubscribed(5000), 0) class MyViewModel( ) : ViewModel() { viewModelScope val data: StateFlow<Int> = }
179. StateFlows with stateIn @Test fun testLazilySharingViewModel() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) assertEquals(0, viewModel.data.value) fakeRepository.emit(1) assertEquals(1, viewModel.data.value) }
180. StateFlows with stateIn @Test fun testLazilySharingViewModel() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) assertEquals(0, viewModel.data.value) fakeRepository.emit(1) assertEquals(1, viewModel.data.value) }
181. StateFlows with stateIn class MyViewModel( myRepository: MyRepository ) : ViewModel() { val data: StateFlow<Int> = myRepository.scores() .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), 0) }
182. StateFlows with stateIn class MyViewModel( myRepository: MyRepository ) : ViewModel() { val data: StateFlow<Int> = myRepository.scores() .stateIn(viewModelScope, , 0) } Test ViewModel Fake Repository SharingStarted.WhileSubscribed(5000)
183. StateFlows with stateIn class MyViewModel( myRepository: MyRepository ) : ViewModel() { val data: StateFlow<Int> = myRepository.scores() .stateIn(viewModelScope, , 0) } Test ViewModel Fake Repository SharingStarted.WhileSubscribed(5000)
184. StateFlows with stateIn class MyViewModel( myRepository: MyRepository ) : ViewModel() { val data: StateFlow<Int> = myRepository.scores() .stateIn(viewModelScope, , 0) } Test ViewModel Fake Repository SharingStarted.WhileSubscribed(5000)
185. StateFlows with stateIn class MyViewModel( myRepository: MyRepository ) : ViewModel() { val data: StateFlow<Int> = myRepository.scores() .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), 0) } Test ViewModel Fake Repository
186. StateFlows with stateIn class MyViewModel( myRepository: MyRepository ) : ViewModel() { val data: StateFlow<Int> = myRepository.scores() .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), 0) } Test ViewModel Fake Repository
187. StateFlows with stateIn class MyViewModel( myRepository: MyRepository ) : ViewModel() { val data: StateFlow<Int> = myRepository.scores() .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), 0) } Test ViewModel Fake Repository
188. StateFlows with stateIn class MyViewModel( myRepository: MyRepository ) : ViewModel() { val data: StateFlow<Int> = myRepository.scores() .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), 0) } Test ViewModel Fake Repository
189. StateFlows with stateIn class MyViewModel( myRepository: MyRepository ) : ViewModel() { val data: StateFlow<Int> = myRepository.scores() .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), 0) } SharingStarted.Lazily Test ViewModel Fake Repository
190. StateFlows with stateIn @Test fun testLazilySharingViewModel() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository) assertEquals(0, viewModel.data.value) fakeRepository.emit(1) assertEquals(1, viewModel.data.value) }
191. StateFlows with stateIn val collectJob = launch(UnconfinedTestDispatcher()) { viewModel.data.collect() } assertEquals(0, viewModel.data.value) fakeRepository.emit(1) assertEquals(1, viewModel.data.value) } collectJob.cancel() @Test fun testLazilySharingViewModel() = runTest { val fakeRepository = HotFakeRepository() val viewModel = MyViewModel(fakeRepository)
192. Summary What did we learn today?
193. Summary • Use runTest for tests with coroutines • Inject dispatchers into your classes to make them testable • Create TestDispatchers as needed, always share a single scheduler • Replace the Main dispatcher in unit tests (also simplifies sharing!)
194. Resources • goo.gle/coroutine-test-guide • goo.gle/flow-test-guide • goo.gle/coroutine-16-migration • github.com/cashapp/turbine NEW!
195. Thank You! Márton Braun @zsmb13 Untangling Coroutine Testing