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Márton Braun @zsmb13
Developer Relations Engineer
Untangling
Coroutine
Testing
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Agenda
● Testing suspending functions
● The coroutine test APIs
● Best practices
● Handling the Main dispatcher
● Flows & StateFlows
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Introduction
What’s up with testing coroutines anyway?
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Introduction
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Introduction
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kotlinx.coroutines.test
Pre-1.6 APIs 1.6+ APIs
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kotlinx.coroutines.test
Pre-1.6 APIs
runBlockingTest
TestCoroutineDispatcher
TestCoroutineScope
pauseDispatcher
resumeDispatcher
1.6+ APIs
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kotlinx.coroutines.test
1.6+ APIs
runTest
TestDispatcher
TestScope
TestCoroutineScheduler
Pre-1.6 APIs
runBlockingTest
TestCoroutineDispatcher
TestCoroutineScope
pauseDispatcher
resumeDispatcher
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kotlinx.coroutines.test
1.6+ APIs
runTest
TestDispatcher
TestScope
TestCoroutineScheduler
Pre-1.6 APIs
runBlockingTest
TestCoroutineDispatcher
TestCoroutineScope
pauseDispatcher
resumeDispatcher
@Experimental
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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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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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kotlinx.coroutines.test
goo.gle/coroutine-test-migration
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Testing suspending functions
runTest. run.
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Testing suspending functions
suspend fun fetchData(): String {
delay(1000L)
return "Hello world"
}
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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Testing new coroutines
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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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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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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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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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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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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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The coroutine test APIs
The latest and greatest in kotlinx.coroutines.test
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Test APIs
runTest
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Test APIs
runTest TestScope
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Test APIs
runTest
TestDispatcher
TestScope
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Test APIs
runTest
TestDispatcher TestCoroutineScheduler
TestScope
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Test APIs
runTest
TestDispatcher TestCoroutineScheduler
TestScope
TestDispatcher
TestDispatcher
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Test APIs
runTest
TestDispatcher TestCoroutineScheduler
TestScope
TestDispatcher
TestDispatcher
All TestDispatchers must share the same scheduler
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Test APIs
TestDispatcher
TestCoroutineScheduler
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Test APIs
TestDispatcher
TestCoroutineScheduler
StandardTestDispatcher UnconfinedTestDispatcher
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StandardTestDispatcher
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●
Queues up coroutines on the scheduler
StandardTestDispatcher
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●
Queues up coroutines on the scheduler
●
You need to advance those coroutines manually
StandardTestDispatcher
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●
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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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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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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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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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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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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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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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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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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●
You need to advance those coroutines manually
StandardTestDispatcher
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●
You need to advance those coroutines manually
StandardTestDispatcher
80
ms
90
ms
100
ms
500
ms
750
ms
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●
You need to advance those coroutines manually
StandardTestDispatcher
80
ms
90
ms
100
ms
500
ms
750
ms
●
runCurrent()
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●
You need to advance those coroutines manually
StandardTestDispatcher
●
runCurrent()
80
ms
90
ms
100
ms
500
ms
750
ms
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●
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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●
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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●
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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●
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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●
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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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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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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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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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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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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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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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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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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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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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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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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UnconfinedTestDispatcher
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UnconfinedTestDispatcher
●
Starts new coroutines eagerly (like runBlockingTest)
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UnconfinedTestDispatcher
●
Starts new coroutines eagerly (like runBlockingTest)
●
Can be a good choice for simple tests
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UnconfinedTestDispatcher
●
Starts new coroutines eagerly (like runBlockingTest)
●
Can be a good choice for simple tests
●
Does not emulate real concurrency
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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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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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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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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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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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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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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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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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TestDispatchers
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TestDispatchers
StandardTestDispatcher
Queues up new coroutines
Use by default
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TestDispatchers
StandardTestDispatcher
Queues up new coroutines
Use by default
UnconfinedTestDispatcher
Starts new coroutines eagerly
Use selectively
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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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Injecting dispatchers
Something something heat exchangers
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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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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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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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Injecting dispatchers
@Test
fun repoTest() = runTest {
val repository = Repository(FakeDatabase())
repository.initialize()
val data = repository.fetchData()
assertEquals("Hello world", data)
}
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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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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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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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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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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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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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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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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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,
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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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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FakeDatabase(),
@Test
fun repoTest() = runTest {
val repository = Repository( )
repository.initialize()
val data = repository.fetchData()
assertEquals("Hello world", data)
}
Injecting dispatchers
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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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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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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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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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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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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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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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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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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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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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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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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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Keeping track of coroutines
Wouldn’t want to lose a Job
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Keeping track of coroutines
●
runTest will wait for coroutines to complete if they are either:
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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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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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Keeping track of coroutines
@Test
fun uncompletedJobs() = runTest {
launch(Dispatchers.IO) {
delay(500L)
// Do some work...
}
}
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Keeping track of coroutines
@Test
fun uncompletedJobs() = runTest(dispatchTimeoutMs = 1000L) {
launch(Dispatchers.IO) {
delay(500L)
// Do some work...
}
}
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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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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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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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Handling the Main dispatcher
A UI thread without a UI
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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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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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Handling the Main dispatcher
}
val viewModel = HomeViewModel()
viewModel.loadMessage()
assertEquals("Greetings!", viewModel.message.value)
@Test
fun testGreeting() = runTest {
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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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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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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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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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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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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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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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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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Managing test objects
Creating dispatchers and schedulers and scopes
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Using TestDispatchers in the test
class Repository(private val ioDispatcher: CoroutineDispatcher) { /* ... */ }
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Using TestDispatchers in the test
class Repository(private val ioDispatcher: CoroutineDispatcher) { /* ... */ }
class DispatcherTypesTest {
@get:Rule
val mainDispatcherRule = MainDispatcherRule()
}
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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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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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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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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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Using TestDispatchers outside the test
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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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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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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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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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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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Creating test objects
class ExampleTest {
runTest {
// ...
}
}
@Test
fun someTest() =
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Creating test objects
class ExampleTest {
)
testScope.runTest {
// ...
}
}
@Test
fun someTest() =
val testScope = TestScope(
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Creating test objects
class ExampleTest {
)
testDispatcher)
testScope.runTest {
// ...
}
}
@Test
fun someTest() =
val testScope = TestScope(
val testDispatcher = StandardTestDispatcher(
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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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Flows
Suspenseful streams
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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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Flows
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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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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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Flows
@Test
fun useTerminalOperators() = runTest {
val repository = Repository(ColdFakeDataSource())
}
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Flows
@Test
fun useTerminalOperators() = runTest {
val repository = Repository(ColdFakeDataSource())
val first = repository.scores().first()
assertEquals(10, first)
}
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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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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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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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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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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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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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Flows
@Test
fun continuouslyCollect() = runTest {
val dataSource = HotFakeDataSource()
val repository = Repository(dataSource)
}
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Flows
@Test
fun continuouslyCollect() = runTest {
val dataSource = HotFakeDataSource()
val repository = Repository(dataSource)
val values = mutableListOf()
}
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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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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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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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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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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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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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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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Flows with Turbine
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Flows with Turbine
@Test
fun usingTurbine() = runTest {
val dataSource = HotFakeDataSource()
val repository = Repository(dataSource)
}
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Flows with Turbine
@Test
fun usingTurbine() = runTest {
val dataSource = HotFakeDataSource()
val repository = Repository(dataSource)
repository.scores().test {
}
}
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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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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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StateFlows
Look! It’s a stream! It’s a state holder!
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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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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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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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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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StateFlows
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StateFlows
class ColdFakeRepository : MyRepository {
override fun scores() = flow {
emit(1)
delay(100)
emit(2)
delay(100)
emit(3)
}
}
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StateFlows
@get:Rule
val mainDispatcherRule = MainDispatcherRule()
@Test
fun testStateFlow() = runTest {
val viewModel = MyViewModel(ColdFakeRepository())
}
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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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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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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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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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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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Summary
What did we learn today?
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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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Resources
● goo.gle/coroutine-test-guide
● goo.gle/coroutine-test-migration
● github.com/cashapp/turbine
NEW!
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Thank You!
Márton Braun
@zsmb13
Untangling Coroutine Testing