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wip: use virtual time for timeout #269

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wip: use virtual time for timeout #269

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dad41df
use virtual time for timeout
mightyguava Sep 24, 2023
570fe47
add a test
mightyguava Sep 24, 2023
7ba8b1f
add new tests suggested by @jingibus
mightyguava Sep 24, 2023
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7 changes: 1 addition & 6 deletions src/commonMain/kotlin/app/cash/turbine/channel.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -94,12 +94,7 @@ private suspend fun <T> withAppropriateTimeout(
timeout: Duration,
block: suspend CoroutineScope.() -> T,
): T {
return if (coroutineContext[TestCoroutineScheduler] != null) {
// withTimeout uses virtual time, which will hang.
withWallclockTimeout(timeout, block)
} else {
withTimeout(timeout, block)
}
return withTimeout(timeout, block)
}

private suspend fun <T> withWallclockTimeout(
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12 changes: 6 additions & 6 deletions src/commonTest/kotlin/app/cash/turbine/ChannelTest.kt
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Expand Up @@ -238,15 +238,15 @@ class ChannelTest {
}

@Test fun awaitHonorsCoroutineContextTimeoutNoTimeout() = runTest {
withTurbineTimeout(1500.milliseconds) {
val job = launch {
neverFlow().collectIntoChannel(this).awaitItem()
}
withContext(Dispatchers.Default) {
withTurbineTimeout(1500.milliseconds) {
val job = launch {
neverFlow().collectIntoChannel(this).awaitItem()
}

withContext(Dispatchers.Default) {
delay(1100)
job.cancel()
}
job.cancel()
}
}

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4 changes: 3 additions & 1 deletion src/commonTest/kotlin/app/cash/turbine/FlowInScopeTest.kt
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Expand Up @@ -208,7 +208,9 @@ class FlowInScopeTest {
delay(1100.milliseconds)
}
}.testIn(this, timeout = 1500.milliseconds)
turbine.awaitComplete()
withContext(Default) {
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Adding these withContext(Default) calls here defeats the entire purpose of these tests.

In any of these tests that uses withContext(Default) within the test subject, the test subject is simulating the experience of an engineer whose code is broken.

If we also run awaitComplete() on the Default dispatcher, we're no longer simulating the experience of that engineer, becuase they won't be calling awaitComplete() on Default: they'll be calling it on TestScope's dispatcher.

This is a critical service that Turbine provides: unlike runTest's timeout, Turbine provides specific feedback on which expected output failed to emit.

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In any of these tests that uses withContext(Default) within the test subject, the test subject is simulating the experience of an engineer whose code is broken.

To clarify this: it simulates this because the engineer literally has a test that is hanging awaiting some value, and their wall clock is ticking.

To me, an interesting test for your change would be something like this:

@Test fun awaitFailsOnVirtualTime() = runTestTurbine {
  assertFailsWith<AssertionError> {
    flow<Nothing> {
      delay(1500.milliseconds)
    }.test(timeout = 1000.milliseconds) {
      awaitComplete()
    }
  }
}

Or:

@Test fun awaitFailsOnVirtualTime() = runTestTurbine {
  assertFailsWith<AssertionError> {
    flow<Nothing> {
      awaitCancellation()
    }.test {
      awaitComplete()
    }
  }
}

...in other words, can we just ditch the wallclock time stuff and rely entirely on virtual time?

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Thanks! I really had no idea what the broken tests were for.

7ba8b1f adds both tests you suggested, both passing.

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can we just ditch the wallclock time stuff and rely entirely on virtual time?

That would be really nice 😄 and also what I'm hoping for.

turbine.awaitComplete()
}
}

@Test fun awaitHonorsCoroutineContextTimeoutTimeout() = runTestTurbine {
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37 changes: 32 additions & 5 deletions src/commonTest/kotlin/app/cash/turbine/FlowTest.kt
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Expand Up @@ -608,6 +608,7 @@ class FlowTest {
flow<Nothing> {
delay(5.seconds)
}.test {
advanceTimeBy(5.seconds)
awaitComplete()
}
}
Expand All @@ -629,13 +630,13 @@ class FlowTest {
}

@Test fun awaitHonorsTestTimeoutNoTimeout() = runTest {
flow<Nothing> {
withContext(Default) {
delay(1100.milliseconds)
flow<Nothing> {
delay(1100.milliseconds)
}.test(timeout = 1500.milliseconds) {
awaitComplete()
}
}
}.test(timeout = 1500.milliseconds) {
awaitComplete()
}
}

@Test fun awaitHonorsCoroutineContextTimeoutTimeout() = runTest {
Expand Down Expand Up @@ -734,6 +735,32 @@ class FlowTest {
}
}

@Test
fun delaysCanBeTested() = runTest {
val took = measureTime {
flow {
delay(5000)
emit("1")
delay(5000)
emit("2")
}.test {
expectNoEvents()

advanceTimeBy(5000)
expectNoEvents()

runCurrent()
assertEquals("1", awaitItem())

val exception = assertFailsWith<AssertionError> {
awaitItem()
}
assertEquals(exception.message, "No value produced in 3s")
}
}
assertTrue(took < 1.seconds, "$took > 1s")
}

@Test
fun timeoutsAreCaptured() = runTest {
flow<Nothing> {
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