Running epollcat IO test on Scalatest

[fede0664]

Running the following test on Scalatest 3.2.14:

class TestIO extends AsyncFunSuite with Matchers {
  implicit val globalRT:IORuntime = epollcat.unsafe.EpollRuntime.global
  override val executionContext = globalRT.compute

  test("IO to Future") {
    val t = IO(true shouldBe true)
    t.unsafeToFuture()
  }
}

The test itself runs successfully:

[info] TestIO:
[info] - IO to Future
[info] Run completed in 13 milliseconds.
[info] Total number of tests run: 1
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 1, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[error] Error during tests:
[error]         TestIO
[error] (testIO / Test / test) sbt.TestsFailedException: Tests unsuccessful

But, as the the [error] lines show, Scalatest fails, reporting this exception on test-reports:

scala.scalanative.testinterface.common.RPCCore$RPCException: java.util.concurrent.TimeoutException: Future timed out after [Duration.Inf]
	at scala.scalanative.testinterface.common.RPCCore.$anonfun$handleMessage$4(RPCCore.scala:66)
	at scala.Option.foreach(Option.scala:407)
	at scala.scalanative.testinterface.common.RPCCore.$anonfun$handleMessage$1(RPCCore.scala:64)
	at scala.scalanative.testinterface.common.RPCCore.$anonfun$handleMessage$1$adapted(RPCCore.scala:43)
	at scala.scalanative.testinterface.common.Serializer$.withInputStream(Serializer.scala:52)
	at scala.scalanative.testinterface.common.RPCCore.handleMessage(RPCCore.scala:43)
	at scala.scalanative.testinterface.NativeRunnerRPC.$anonfun$runner$1(NativeRunnerRPC.scala:31)
	at scala.scalanative.testinterface.NativeRunnerRPC.$anonfun$runner$1$adapted(NativeRunnerRPC.scala:31)
	at scala.scalanative.testinterface.ComRunner$$anon$1.run(ComRunner.scala:61)

Any suggestion on how to test an epollcat based IO on Scalatest?
Similar test on MUnit runs ok.

[armanbilge]

Thanks for the report. I am not very familiar with Scalatest, but this is not an issue specific to epollcat. For example this also fails with the same error. This suggests that Scalatest native is unable to support custom ExecutionContexts (even if it's the Scala global EC).

//> using lib "org.scalatest::scalatest::3.2.14"
//> using platform "native"

import org.scalatest.funsuite._
import org.scalatest.matchers.should._
import scala.concurrent.{ExecutionContext, Future}

class Bugged extends AsyncFunSuite with Matchers {
  override val executionContext = ExecutionContext.global
  test("just a future") {
    Future(true shouldBe true)(executionContext)
  }
}

$ scala-cli test bug.scala 
Bugged:
- just a future
Error: scala.scalanative.testinterface.common.RPCCore$RPCException: java.util.concurrent.TimeoutException: Future timed out after [Duration.Inf]
For more details, please see '/workspace/sandbox/.scala-build/stacktraces/1666892867-15812559970291505116.log'
Test runner interrupted by fatal signal 9

[fede0664]

Thanks for looking at this.
I just tried a regular class outside Scalatest and I'm getting the same exception:

import scala.concurrent.Await
import scala.concurrent.duration.Duration
import cats.effect.unsafe.IORuntime
import cats.effect.IO

object Main {
  @main def run: Unit = {
    implicit val globalRT:IORuntime = epollcat.unsafe.EpollRuntime.global
    val executionContext = globalRT.compute    
    val t = IO.delay(true)
    Await.result(t.unsafeToFuture(), Duration.Inf)
  }
}

java.util.concurrent.TimeoutException: Future timed out after [Duration.Inf]
        at java.lang.StackTrace$.currentStackTrace(Unknown Source)
        at java.lang.Throwable.fillInStackTrace(Unknown Source)
        at scala.concurrent.impl.Promise$DefaultPromise.tryAwait0(Unknown Source)
        at scala.concurrent.impl.Promise$DefaultPromise.result(Unknown Source)
        at scala.concurrent.Await$.$anonfun$result$1(Unknown Source)
        at scala.concurrent.Await$$$Lambda$2.apply(Unknown Source)
        at scala.concurrent.BlockContext$DefaultBlockContext$.blockOn(Unknown Source)
        at scala.concurrent.package$.blocking(Unknown Source)
        at scala.concurrent.Await$.result(Unknown Source)
        at Main$.run(Unknown Source)
        at run.main(Unknown Source)
        at <none>.main(Unknown Source)
        at <none>.(Unknown Source)
        at <none>.__libc_start_main(Unknown Source)
        at <none>._start(Unknown Source)

Does epollcat support the Await pattern?
It seems that Scalatest uses this same pattern inside AsyncFunSuite

[armanbilge]

Does epollcat support the Await pattern?

Again, this is not specific to epollcat :) the fundamental issue here is that Scala Native itself does not support Await. This is because it is a single-threaded runtime, and Await requires blocking.

//> using platform "native"

import scala.concurrent.{Await, ExecutionContext, Future}
import scala.concurrent.duration.Duration

object Main {
  @main def run: Unit = {
    val t = Future(true)(ExecutionContext.global)
    Await.result(t, Duration.Inf)
  }
}