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Fix flakey test (issue 45) #67

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Fix flakey test (issue 45) #67

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34 changes: 21 additions & 13 deletions molecule/molecule-runtime/src/commonTest/java/app/cash/molecule/MoleculeTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,12 @@ import org.junit.Test
import kotlin.coroutines.CoroutineContext
import kotlin.test.assertFailsWith
import kotlin.time.ExperimentalTime
import kotlinx.coroutines.async
import kotlinx.coroutines.channels.Channel
import kotlinx.coroutines.channels.Channel.Factory.UNLIMITED
import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.withContext
import kotlinx.coroutines.withTimeout

@ExperimentalCoroutinesApi
@ExperimentalTime
Expand Down Expand Up @@ -102,31 +108,33 @@ class MoleculeTest {
override val key get() = CoroutineExceptionHandler
}

@Test fun errorDelayed() {
val dispatcher = TestCoroutineDispatcher()
@Test fun errorDelayed() = runBlocking {
val clock = BroadcastFrameClock()
val exceptionHandler = RecordingExceptionHandler()
val scope = CoroutineScope(dispatcher + clock + exceptionHandler)
var value: Int? = null
val values = Channel<Int>(UNLIMITED)

// Use a custom subtype to prevent coroutines from breaking referential equality.
val runtimeException = object : RuntimeException() {}
var count by mutableStateOf(0)
scope.launchMolecule(emitter = { value = it }) {
if (count == 1) {
throw runtimeException
}
count
val exception = async {
runCatching {
withContext(clock) {
launchMolecule(emitter = values::trySend) {
if (count == 1) {
throw runtimeException
}
count
}
}
}.exceptionOrNull()
}

assertEquals(0, value)
assertEquals(0, withTimeout(1000) { values.receive() })

count++
Snapshot.sendApplyNotifications() // Ensure external state mutation is observed.
clock.sendFrame(0)
assertSame(runtimeException, exceptionHandler.exceptions.single())

scope.cancel()
assertSame(runtimeException, withTimeout(1000) { exception.await() })
}

@Test fun errorInEffect() {
Expand Down
15 changes: 10 additions & 5 deletions molecule/molecule-runtime/src/main/java/app/cash/molecule/molecule.kt
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Expand Up @@ -24,10 +24,14 @@ import androidx.compose.runtime.snapshots.Snapshot
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.CoroutineStart.UNDISPATCHED
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.channels.Channel
import kotlinx.coroutines.channels.Channel.Factory.CONFLATED
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.channelFlow
import kotlinx.coroutines.flow.collect
import kotlinx.coroutines.flow.consumeAsFlow
import kotlinx.coroutines.job
import kotlinx.coroutines.launch

Expand Down Expand Up @@ -89,7 +93,12 @@ fun <T> CoroutineScope.launchMolecule(
body: @Composable () -> T,
) {
val recomposer = Recomposer(coroutineContext)
val composition = Composition(UnitApplier, recomposer)
Composition(UnitApplier, recomposer).apply {
setContent {
emitter(body())
}
}

launch(start = UNDISPATCHED) {
recomposer.runRecomposeAndApplyChanges()
}
Expand All @@ -107,10 +116,6 @@ fun <T> CoroutineScope.launchMolecule(
coroutineContext.job.invokeOnCompletion {
snapshotHandle.dispose()
}

composition.setContent {
emitter(body())
}
}

private object UnitApplier : AbstractApplier<Unit>(Unit) {
Expand Down