Untangling Coroutine Testing (Android Makers 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.

Transcript

1. Márton Braun @zsmb13
   Developer Relations Engineer
   Untangling
   Coroutine
   Testing
   

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2. Agenda
   ● Testing suspending functions
   ● The coroutine test APIs
   ● Best practices
   ● Handling the Main dispatcher
   ● Flows & StateFlows
   

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3. Introduction
   What’s up with testing coroutines anyway?
   

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4. Introduction
   

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5. Introduction
   

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6. kotlinx.coroutines.test
   Pre-1.6 APIs 1.6+ APIs
   

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7. kotlinx.coroutines.test
   Pre-1.6 APIs
   runBlockingTest
   TestCoroutineDispatcher
   TestCoroutineScope
   pauseDispatcher
   resumeDispatcher
   1.6+ APIs
   

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8. kotlinx.coroutines.test
   1.6+ APIs
   runTest
   TestDispatcher
   TestScope
   TestCoroutineScheduler
   Pre-1.6 APIs
   runBlockingTest
   TestCoroutineDispatcher
   TestCoroutineScope
   pauseDispatcher
   resumeDispatcher
   

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9. kotlinx.coroutines.test
   1.6+ APIs
   runTest
   TestDispatcher
   TestScope
   TestCoroutineScheduler
   Pre-1.6 APIs
   runBlockingTest
   TestCoroutineDispatcher
   TestCoroutineScope
   pauseDispatcher
   resumeDispatcher
   @Experimental
   

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10. kotlinx.coroutines.test
    1.6+ APIs
    runTest
    TestDispatcher
    TestScope
    TestCoroutineScheduler
    Pre-1.6 APIs
    runBlockingTest
    TestCoroutineDispatcher
    TestCoroutineScope
    pauseDispatcher
    resumeDispatcher
    @Experimental
    @Deprecated
    

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11. kotlinx.coroutines.test
    1.6+ APIs
    runTest
    TestDispatcher
    TestScope
    TestCoroutineScheduler
    Pre-1.6 APIs
    runBlockingTest
    TestCoroutineDispatcher
    TestCoroutineScope
    pauseDispatcher
    resumeDispatcher
    @Experimental
    @Deprecated
    @Experimental
    

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12. kotlinx.coroutines.test
    goo.gle/coroutine-test-migration
    

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13. Testing suspending functions
    runTest. run.
    

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14. Testing suspending functions
    suspend fun fetchData(): String {
    delay(1000L)
    return "Hello world"
    }
    

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15. Testing suspending functions
    suspend fun fetchData(): String {
    delay(1000L)
    return "Hello world"
    }
    @Test
    fun dataIsHelloWorld() {
    val data = fetchData()
    assertEquals("Hello world", data)
    }
    

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16. Testing suspending functions
    suspend fun fetchData(): String {
    delay(1000L)
    return "Hello world"
    }
    @Test
    fun dataIsHelloWorld() {
    val data = fetchData()
    assertEquals("Hello world", data)
    }
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    *
    

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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
    

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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()
    

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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()
    

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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()
    

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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()
    

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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()
    

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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()
    

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31. Testing new coroutines
    

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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()
    )
    }
    

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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()
    )
    }
    

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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()
    )
    }
    

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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()
    )
    }
    

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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()
    )
    }
    

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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()
    )
    }
    

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38. The coroutine test APIs
    The latest and greatest in kotlinx.coroutines.test
    

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39. Test APIs
    runTest
    

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40. Test APIs
    runTest TestScope
    

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41. Test APIs
    runTest
    TestDispatcher
    TestScope
    

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42. Test APIs
    runTest
    TestDispatcher TestCoroutineScheduler
    TestScope
    

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43. Test APIs
    runTest
    TestDispatcher TestCoroutineScheduler
    TestScope
    TestDispatcher
    TestDispatcher
    

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44. Test APIs
    runTest
    TestDispatcher TestCoroutineScheduler
    TestScope
    TestDispatcher
    TestDispatcher
    All TestDispatchers must share the same scheduler
    

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45. Test APIs
    TestDispatcher
    TestCoroutineScheduler
    

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46. Test APIs
    TestDispatcher
    TestCoroutineScheduler
    StandardTestDispatcher UnconfinedTestDispatcher
    

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47. StandardTestDispatcher
    

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48. ●
    Queues up coroutines on the scheduler
    StandardTestDispatcher
    

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49. ●
    Queues up coroutines on the scheduler
    ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    

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50. ●
    Queues up coroutines on the scheduler
    ●
    You need to advance those coroutines manually
    ●
    runTest uses a StandardTestDispatcher by default
    StandardTestDispatcher
    runTest
    StandardTestDispatcher
    TestScope
    

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51. StandardTestDispatcher
    @Test
    fun standardTest() = runTest {
    val repo = UserRepository()
    launch { repo.register("Alice") }
    launch { repo.register("Bob") }
    assertEquals(listOf("Alice", "Bob"), repo.getAllUsers())
    }
    

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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
    

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53. StandardTestDispatcher
    @Test
    fun standardTest() = runTest {
    val repo = UserRepository()
    launch { repo.register("Alice") }
    launch { repo.register("Bob") }
    assertEquals(listOf("Alice", "Bob"), repo.getAllUsers())
    }
    

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54. StandardTestDispatcher
    @Test
    fun standardTest() = runTest {
    val repo = UserRepository()
    launch { repo.register("Alice") }
    launch { repo.register("Bob") }
    assertEquals(listOf("Alice", "Bob"), repo.getAllUsers())
    }
    UserRepo()
    

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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")
    

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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("Alice") reg("Bob")
    

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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("Alice") reg("Bob")
    

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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("Alice") reg("Bob")
    

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59. ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    

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60. ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    80
    ms
    90
    ms
    100
    ms
    500
    ms
    750
    ms
    

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61. ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    80
    ms
    90
    ms
    100
    ms
    500
    ms
    750
    ms
    ●
    runCurrent()
    

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62. ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    ●
    runCurrent()
    80
    ms
    90
    ms
    100
    ms
    500
    ms
    750
    ms
    

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63. ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    ●
    runCurrent()
    ●
    advanceTimeBy(delayTimeMillis: Long)
    80
    ms
    90
    ms
    100
    ms
    500
    ms
    750
    ms
    

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64. ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    ●
    runCurrent()
    ●
    advanceTimeBy(delayTimeMillis: Long)
    80
    ms
    90
    ms
    100
    ms
    500
    ms
    750
    ms
    

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65. ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    ●
    runCurrent()
    ●
    advanceTimeBy(delayTimeMillis: Long)
    80
    ms
    90
    ms
    100
    ms
    500
    ms
    750
    ms
    

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66. ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    ●
    runCurrent()
    ●
    advanceTimeBy(delayTimeMillis: Long)
    ●
    advanceUntilIdle()
    80
    ms
    90
    ms
    100
    ms
    500
    ms
    750
    ms
    

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67. ●
    You need to advance those coroutines manually
    StandardTestDispatcher
    ●
    runCurrent()
    ●
    advanceTimeBy(delayTimeMillis: Long)
    ●
    advanceUntilIdle()
    80
    ms
    90
    ms
    100
    ms
    500
    ms
    750
    ms
    

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68. StandardTestDispatcher
    @Test
    fun standardTest() = runTest {
    val repo = UserRepository()
    launch { repo.register("Alice") }
    launch { repo.register("Bob") }
    assertEquals(listOf("Alice", "Bob"), repo.getAllUsers())
    }
    

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69. StandardTestDispatcher
    @Test
    fun standardTest() = runTest {
    val repo = UserRepository()
    launch { repo.register("Alice") }
    launch { repo.register("Bob") }
    advanceUntilIdle()
    assertEquals(listOf("Alice", "Bob"), repo.getAllUsers())
    }
    

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70. StandardTestDispatcher
    @Test
    fun standardTest() = runTest {
    val repo = UserRepository()
    launch { repo.register("Alice") }
    launch { repo.register("Bob") }
    advanceUntilIdle()
    assertEquals(listOf("Alice", "Bob"), repo.getAllUsers())
    }
    

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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()
    

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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")
    

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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("Alice") reg("Bob")
    

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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")
    

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75. 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")
    

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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")
    

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77. 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()
    

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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()
    

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79. UnconfinedTestDispatcher
    

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80. UnconfinedTestDispatcher
    ●
    Starts new coroutines eagerly (like runBlockingTest)
    

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81. UnconfinedTestDispatcher
    ●
    Starts new coroutines eagerly (like runBlockingTest)
    ●
    Can be a good choice for simple tests
    

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82. UnconfinedTestDispatcher
    ●
    Starts new coroutines eagerly (like runBlockingTest)
    ●
    Can be a good choice for simple tests
    ●
    Does not emulate real concurrency
    

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83. UnconfinedTestDispatcher
    @Test
    fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) {
    val userRepo = UserRepository()
    launch { userRepo.register("Alice") }
    launch { userRepo.register("Bob") }
    assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers())
    }
    

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84. UnconfinedTestDispatcher
    @Test
    fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) {
    val userRepo = UserRepository()
    launch { userRepo.register("Alice") }
    launch { userRepo.register("Bob") }
    assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers())
    }
    

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85. 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
    

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86. UnconfinedTestDispatcher
    @Test
    fun unconfinedTest() = runTest(UnconfinedTestDispatcher()) {
    val userRepo = UserRepository()
    launch { userRepo.register("Alice") }
    launch { userRepo.register("Bob") }
    assertEquals(listOf("Alice", "Bob"), userRepo.getAllUsers())
    }
    UserRepo()
    

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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() reg("Alice")
    

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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") reg("Bob")
    

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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") assert()
    

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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()
    

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91. TestDispatchers
    

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92. TestDispatchers
    StandardTestDispatcher
    Queues up new coroutines
    Use by default
    

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93. TestDispatchers
    StandardTestDispatcher
    Queues up new coroutines
    Use by default
    UnconfinedTestDispatcher
    Starts new coroutines eagerly
    Use selectively
    

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94. TestDispatchers
    StandardTestDispatcher
    Queues up new coroutines
    Use by default
    UnconfinedTestDispatcher
    Starts new coroutines eagerly
    Use selectively
    • While migrating tests from old APIs
    • As the Main dispatcher
    • For coroutines that collect values
    

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95. Injecting dispatchers
    Something something heat exchangers
    

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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()
    }
    }
    

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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()
    }
    }
    

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98. 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()
    }
    }
    

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99. Injecting dispatchers
    @Test
    fun repoTest() = runTest {
    val repository = Repository(FakeDatabase())
    repository.initialize()
    val data = repository.fetchData()
    assertEquals("Hello world", data)
    }
    

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100. Injecting dispatchers
     @Test
     fun repoTest() = runTest {
     val repository = Repository(FakeDatabase())
     repository.initialize()
     val data = repository.fetchData()
     assertEquals("Hello world", data)
     }
     Test thread
     Dispatchers.IO
     

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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
     

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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.populate()
     fun initialize() {
     scope.launch {
     database.populate()
     }
     }
     

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103. 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()
     }
     

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104. 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()
     

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105. 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)
     }
     

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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)
     }
     

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107. 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)
     }
     

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108. ,
     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
     

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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
     ,
     

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110. FakeDatabase(),
     @Test
     fun repoTest() = runTest {
     val repository = Repository( )
     repository.initialize()
     val data = repository.fetchData()
     assertEquals("Hello world", data)
     }
     Injecting dispatchers
     

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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()
     

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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
     

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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)
     }
     

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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(...)
     

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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)
     }
     Repo(...)
     db.populate()
     fun initialize() {
     scope.launch {
     database.populate()
     }
     }
     

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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)
     }
     db.populate()
     Repo(...)
     

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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()
     

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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() db.read()
     suspend fun fetchData() =
     withContext(ioDispatcher) {
     database.read()
     }
     

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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() assert()
     

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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)
     }
     fun initialize() {
     scope.launch {
     database.populate()
     }
     }
     This is a bad API, don’t do this
     

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121. 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 {
     return scope.async {
     }
     }
     database.populate()
     

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122. 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()
     

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123. Keeping track of coroutines
     Wouldn’t want to lose a Job
     

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124. Keeping track of coroutines
     ●
     runTest will wait for coroutines to complete if they are either:
     

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125. Keeping track of coroutines
     ●
     runTest will wait for coroutines to complete if they are either:
     ●
     Children of the test coroutine (up to a timeout)
     

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126. Keeping track of coroutines
     ●
     runTest will wait for coroutines to complete if they are either:
     ●
     Children of the test coroutine (up to a timeout)
     ●
     Running on the test scheduler
     

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127. Keeping track of coroutines
     @Test
     fun uncompletedJobs() = runTest {
     launch(Dispatchers.IO) {
     delay(500L)
     // Do some work...
     }
     }
     

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128. Keeping track of coroutines
     @Test
     fun uncompletedJobs() = runTest(dispatchTimeoutMs = 1000L) {
     launch(Dispatchers.IO) {
     delay(500L)
     // Do some work...
     }
     }
     

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129. Keeping track of coroutines
     class SocketService(private val ioDispatcher: CoroutineDispatcher) {
     private val scope = CoroutineScope(ioDispatcher)
     fun shutdown() {
     scope.launch {
     // Do some async cleanup
     }
     }
     }
     

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130. Keeping track of coroutines
     @Test
     fun cleanupTest() = runTest {
     val testDispatcher = StandardTestDispatcher(testScheduler)
     val service = SocketService(testDispatcher)
     // Do some testing...
     service.shutdown()
     }
     fun shutdown() {
     scope.launch {
     // Do some async cleanup
     }
     }
     

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131. Keeping track of coroutines
     @Test
     fun cleanupTest() = runTest {
     val testDispatcher = StandardTestDispatcher(testScheduler)
     val service = SocketService(testDispatcher)
     // Do some testing...
     service.shutdown()
     }
     this: TestScope
     fun shutdown() {
     scope.launch {
     // Do some async cleanup
     }
     }
     

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132. Handling the Main dispatcher
     A UI thread without a UI
     

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133. Handling the Main dispatcher
     class HomeViewModel : ViewModel() {
     private val _message = MutableStateFlow("")
     val message: StateFlow get() = _message
     fun loadMessage() {
     viewModelScope.launch {
     _message.value = "Greetings!"
     }
     }
     }
     

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134. Handling the Main dispatcher
     class HomeViewModel : ViewModel() {
     private val _message = MutableStateFlow("")
     val message: StateFlow get() = _message
     fun loadMessage() {
     viewModelScope.launch {
     _message.value = "Greetings!"
     }
     }
     }
     

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135. Handling the Main dispatcher
     }
     val viewModel = HomeViewModel()
     viewModel.loadMessage()
     assertEquals("Greetings!", viewModel.message.value)
     @Test
     fun testGreeting() = runTest {
     

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136. 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 {
     

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137. 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 {
     

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138. 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()
     }
     }
     

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139. 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!"
     }
     }
     

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140. 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()
     

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141. 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()
     

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142. 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)
     }
     }
     

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143. 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)
     }
     }
     If you replace the Main dispatcher with a TestDispatcher,
     all new TestDispatchers will automatically share its scheduler
     

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144. Managing test objects
     Creating dispatchers and schedulers and scopes
     

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145. Using TestDispatchers in the test
     class Repository(private val ioDispatcher: CoroutineDispatcher) { /* ... */ }
     

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146. Using TestDispatchers in the test
     class Repository(private val ioDispatcher: CoroutineDispatcher) { /* ... */ }
     class DispatcherTypesTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     }
     

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147. Using TestDispatchers in the test
     class Repository(private val ioDispatcher: CoroutineDispatcher) { /* ... */ }
     class DispatcherTypesTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun injectingTestDispatchers() = runTest { // Shares Main’s scheduler
     }
     }
     

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148. Using TestDispatchers in the test
     class Repository(private val ioDispatcher: CoroutineDispatcher) { /* ... */ }
     class DispatcherTypesTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun injectingTestDispatchers() = runTest {
     val unconfinedRepo = Repository(mainDispatcherRule.testDispatcher)
     }
     }
     

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149. Using TestDispatchers in the test
     class Repository(private val ioDispatcher: CoroutineDispatcher) { /* ... */ }
     class DispatcherTypesTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun injectingTestDispatchers() = runTest {
     val unconfinedRepo = Repository(mainDispatcherRule.testDispatcher)
     val standardRepo = Repository(StandardTestDispatcher())
     } // ^ Shares Main’s scheduler
     }
     

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150. Using TestDispatchers in the test
     class Repository(private val ioDispatcher: CoroutineDispatcher) { /* ... */ }
     class DispatcherTypesTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun injectingTestDispatchers() = runTest {
     val unconfinedRepo = Repository(UnconfinedTestDispatcher())
     val standardRepo = Repository(StandardTestDispatcher())
     }
     }
     

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151. Using TestDispatchers outside the test
     

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152. Using TestDispatchers outside the test
     class RepositoryTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     private val repository = Repository(???)
     @Test
     fun someRepositoryTest() = runTest {
     // Test the repository...
     }
     }
     

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153. Using TestDispatchers outside the test
     class RepositoryTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     private val repository = Repository(UnconfinedTestDispatcher())
     @Test
     fun someRepositoryTest() = runTest {
     // Test the repository...
     }
     }
     

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154. Using TestDispatchers outside the test
     class RepositoryTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     private val repository = Repository(UnconfinedTestDispatcher())
     }
     @Test
     fun someRepositoryTest() = runTest {
     // Test the repository...
     }
     

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155. Using TestDispatchers outside the test
     class RepositoryTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     private val repository = Repository( )
     }
     @Test
     fun someRepositoryTest() = runTest {
     // Test the repository...
     }
     mainDispatcherRule.testDispatcher
     

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156. Using TestDispatchers outside the test
     class RepositoryTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     private val repository = Repository(
     StandardTestDispatcher( .scheduler)
     )
     }
     @Test
     fun someRepositoryTest() = runTest {
     // Test the repository...
     }
     mainDispatcherRule.testDispatcher
     

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157. Creating test objects
     class ExampleTest {
     runTest {
     // ...
     }
     }
     @Test
     fun someTest() =
     

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158. Creating test objects
     class ExampleTest {
     )
     testScope.runTest {
     // ...
     }
     }
     @Test
     fun someTest() =
     val testScope = TestScope(
     

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159. Creating test objects
     class ExampleTest {
     )
     testDispatcher)
     testScope.runTest {
     // ...
     }
     }
     @Test
     fun someTest() =
     val testScope = TestScope(
     val testDispatcher = StandardTestDispatcher(
     

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160. Creating test objects
     class ExampleTest {
     val testScheduler = TestCoroutineScheduler()
     testScheduler)
     testDispatcher)
     testScope.runTest {
     // ...
     }
     }
     @Test
     fun someTest() =
     val testScope = TestScope(
     val testDispatcher = StandardTestDispatcher(
     

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161. Flows
     Suspenseful streams
     

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162. Flows
     interface DataSource {
     fun counts(): Flow
     }
     class Repository(private val dataSource: DataSource) {
     fun scores(): Flow {
     return dataSource.counts().map { it * 10 }
     }
     }
     

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163. Flows
     

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164. Flows
     interface DataSource {
     fun counts(): Flow
     }
     class Repository(private val dataSource: DataSource) {
     fun scores(): Flow {
     return dataSource.counts().map { it * 10 }
     }
     }
     

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165. Flows
     interface DataSource {
     fun counts(): Flow
     }
     class Repository(private val dataSource: DataSource) {
     fun scores(): Flow {
     return dataSource.counts().map { it * 10 }
     }
     }
     class ColdFakeDataSource : DataSource {
     override fun counts(): Flow {
     return flowOf(1, 2, 3, 4)
     }
     }
     

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166. Flows
     @Test
     fun useTerminalOperators() = runTest {
     val repository = Repository(ColdFakeDataSource())
     }
     

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167. Flows
     @Test
     fun useTerminalOperators() = runTest {
     val repository = Repository(ColdFakeDataSource())
     val first = repository.scores().first()
     assertEquals(10, first)
     }
     

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168. 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)
     }
     

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169. 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])
     }
     

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170. Flows
     class HotFakeDataSource : DataSource {
     private val flow = MutableSharedFlow()
     suspend fun emit(value: Int) = flow.emit(value)
     override fun counts(): Flow = flow
     }
     

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171. Flows
     class HotFakeDataSource : DataSource {
     private val flow = MutableSharedFlow()
     suspend fun emit(value: Int) = flow.emit(value)
     override fun counts(): Flow = flow
     }
     

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172. Flows
     class HotFakeDataSource : DataSource {
     private val flow = MutableSharedFlow()
     suspend fun emit(value: Int) = flow.emit(value)
     override fun counts(): Flow = flow
     }
     

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173. Flows
     class HotFakeDataSource : DataSource {
     private val flow = MutableSharedFlow()
     suspend fun emit(value: Int) = flow.emit(value)
     override fun counts(): Flow = flow
     }
     

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174. Flows
     @Test
     fun continuouslyCollect() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     }
     

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175. Flows
     @Test
     fun continuouslyCollect() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     val values = mutableListOf()
     }
     

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176. Flows
     @Test
     fun continuouslyCollect() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     val values = mutableListOf()
     val collectJob = launch(UnconfinedTestDispatcher()) {
     repository.scores().collect {
     values += it
     }
     }
     }
     

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177. Flows
     @Test
     fun continuouslyCollect() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     val values = mutableListOf()
     val collectJob = launch(UnconfinedTestDispatcher()) {
     repository.scores().collect {
     values += it
     }
     }
     }
     

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178. Flows
     @Test
     fun continuouslyCollect() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     val values = mutableListOf()
     val collectJob = launch(UnconfinedTestDispatcher()) {
     repository.scores().collect {
     values += it
     }
     }
     }
     

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179. Flows
     @Test
     fun continuouslyCollect() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     val values = mutableListOf()
     val collectJob = launch(UnconfinedTestDispatcher()) {
     repository.scores().toList(values)
     }
     }
     

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180. Flows
     @Test
     fun continuouslyCollect() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     val values = mutableListOf()
     val collectJob = launch(UnconfinedTestDispatcher()) {
     repository.scores().toList(values)
     }
     dataSource.emit(1)
     assertEquals(10, values[0])
     }
     

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181. Flows
     @Test
     fun continuouslyCollect() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     val values = mutableListOf()
     val collectJob = launch(UnconfinedTestDispatcher()) {
     repository.scores().toList(values)
     }
     dataSource.emit(1)
     assertEquals(10, values[0])
     }
     collectJob.cancel()
     

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182. Flows
     @Test
     fun continuouslyCollect() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     val values = mutableListOf()
     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()
     

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183. Flows with Turbine
     

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184. Flows with Turbine
     @Test
     fun usingTurbine() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     }
     

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185. Flows with Turbine
     @Test
     fun usingTurbine() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     repository.scores().test {
     }
     }
     

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186. Flows with Turbine
     @Test
     fun usingTurbine() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     repository.scores().test {
     dataSource.emit(1)
     assertEquals(10, awaitItem())
     }
     }
     

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187. Flows with Turbine
     @Test
     fun usingTurbine() = runTest {
     val dataSource = HotFakeDataSource()
     val repository = Repository(dataSource)
     repository.scores().test {
     dataSource.emit(1)
     assertEquals(10, awaitItem())
     dataSource.emit(2)
     awaitItem()
     dataSource.emit(3)
     assertEquals(30, awaitItem())
     }
     }
     

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188. StateFlows
     Look! It’s a stream! It’s a state holder!
     

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189. interface MyRepository {
     fun scores(): Flow
     }
     class MyViewModel(private val myRepository: MyRepository) : ViewModel() {
     private val _data = MutableStateFlow(0)
     val data: StateFlow = _data.asStateFlow()
     fun initialize() {
     viewModelScope.launch {
     myRepository.scores().collect { score ->
     _data.value = score
     }
     }
     }
     }
     StateFlows
     

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190. interface MyRepository {
     fun scores(): Flow
     }
     class MyViewModel(private val myRepository: MyRepository) : ViewModel() {
     private val _data = MutableStateFlow(0)
     val data: StateFlow = _data.asStateFlow()
     fun initialize() {
     viewModelScope.launch {
     myRepository.scores().collect { score ->
     _data.value = score
     }
     }
     }
     }
     StateFlows
     

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191. interface MyRepository {
     fun scores(): Flow
     }
     class MyViewModel(private val myRepository: MyRepository) : ViewModel() {
     private val _data = MutableStateFlow(0)
     val data: StateFlow = _data.asStateFlow()
     fun initialize() {
     viewModelScope.launch {
     myRepository.scores().collect { score ->
     _data.value = score
     }
     }
     }
     }
     StateFlows
     

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192. interface MyRepository {
     fun scores(): Flow
     }
     class MyViewModel(private val myRepository: MyRepository) : ViewModel() {
     private val _data = MutableStateFlow(0)
     val data: StateFlow = _data.asStateFlow()
     fun initialize() {
     viewModelScope.launch {
     myRepository.scores().collect { score ->
     _data.value = score
     }
     }
     }
     }
     StateFlows
     

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193. StateFlows
     

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194. StateFlows
     class ColdFakeRepository : MyRepository {
     override fun scores() = flow {
     emit(1)
     delay(100)
     emit(2)
     delay(100)
     emit(3)
     }
     }
     

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195. StateFlows
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun testStateFlow() = runTest {
     val viewModel = MyViewModel(ColdFakeRepository())
     }
     

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196. StateFlows
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun testStateFlow() = runTest {
     val viewModel = MyViewModel(ColdFakeRepository())
     viewModel.initialize()
     }
     fun initialize() {
     viewModelScope.launch {
     myRepository.scores().collect { score ->
     _data.value = score
     }
     }
     }
     

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197. StateFlows
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun testStateFlow() = runTest {
     val viewModel = MyViewModel(ColdFakeRepository())
     viewModel.initialize()
     assertEquals(1, viewModel.data.value)
     }
     

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198. StateFlows
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun testStateFlow() = runTest {
     val viewModel = MyViewModel(ColdFakeRepository())
     viewModel.initialize()
     assertEquals(1, viewModel.data.value)
     advanceTimeBy(101)
     assertEquals(2, viewModel.data.value)
     }
     

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199. StateFlows
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun testStateFlow() = runTest {
     val viewModel = MyViewModel(ColdFakeRepository())
     viewModel.initialize()
     assertEquals(1, viewModel.data.value)
     advanceTimeBy(101)
     assertEquals(2, viewModel.data.value)
     advanceTimeBy(101)
     assertEquals(3, viewModel.data.value)
     }
     

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200. StateFlows
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
     @Test
     fun testStateFlow() = runTest {
     val viewModel = MyViewModel(ColdFakeRepository())
     viewModel.initialize()
     assertEquals(1, viewModel.data.value)
     advanceTimeBy(101)
     assertEquals(2, viewModel.data.value)
     advanceTimeBy(101)
     assertEquals(3, viewModel.data.value)
     }
     

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201. Summary
     What did we learn today?
     

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202. 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!)
     

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203. Resources
     ● goo.gle/coroutine-test-guide
     ● goo.gle/coroutine-test-migration
     ● github.com/cashapp/turbine
     NEW!
     

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204. Thank You!
     Márton Braun
     @zsmb13
     Untangling Coroutine Testing
     

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