Feature request: Integration with cats-effect-testkit

[morgen-peschke]

Code using cats-effect-testkit has a rough transition to the CatsEffectAssertions, as either a bunch of extra wrapping needs added around the value passed to .assertEquals, or the returned Option[Outcome[F, E, A]] needs unwrapped before in can be checked.

Example:

import cats.effect.IO
import cats.effect.kernel.Outcome
import cats.effect.testkit.TestControl
import cats.syntax.all._
import munit.CatsEffectSuite

import scala.concurrent.duration.DurationInt

class FooSpec extends CatsEffectSuite {
  test("wrapping") {
    val test =
      for {
        start <- IO.realTimeInstant
        _ <- IO.sleep(5.seconds)
        _ <- IO.realTimeInstant.assertEquals(start.plusSeconds(5))
      } yield 5

    TestControl.execute(test)
      .flatMap { control =>
        control.tickFor(6.seconds) *> control.results
      }
      // Unfortunately, the type annotations do appear to be needed
      .assertEquals(Outcome.Succeeded[cats.Id, Throwable, Int](5).some)
  }

  test("un-wrapping") {
    val test =
      for {
        start <- IO.realTimeInstant
        _ <- IO.sleep(5.seconds)
        _ <- IO.realTimeInstant.assertEquals(start.plusSeconds(5))
      } yield 5

    TestControl.execute(test)
      .flatMap { control =>
        control.tickFor(6.seconds) *> control.results
      }
      .flatMap {
        case Some(Outcome.Succeeded(value)) => value.pure[IO]
        case other => fail("Outcome was not a success", clues(other))
      }
      .assertEquals(5)
  }
}

Something along these lines might be a useful addition (with MUnitCatsAssertionsForIOOutcomeOps):

def outcomeIntercept[T <: Throwable](outcome: Option[Outcome[?, Throwable, ?]],
                                     clues: Clues = new Clues(Nil)
                                    )(implicit T: ClassTag[T], loc: Location): IO[Throwable] =
  outcome match {
    case None => IO[Throwable](fail("Outcome did not contain a value", clues))
    case Some(Outcome.Canceled()) => IO[Throwable](fail("Outcome was cancellation instead of error", clues))
    case Some(Outcome.Succeeded(fa)) =>
      IO[Throwable](fail(
        "Outcome was success instead of error",
        // This should be OK because `F` will usually be cats.Id
        new Clues(new Clue("returned", fa, fa.getClass.getTypeName) :: clues.values)
      ))
    case Some(Outcome.Errored(e)) =>
      e match {
        case e: munit.FailExceptionLike[_] if !T.runtimeClass.isAssignableFrom(e.getClass) =>
          IO.raiseError(e)
        case e if T.runtimeClass.isAssignableFrom(e.getClass) => e.pure[IO]
        case e =>
          val obtained = e.getClass.getName
          val expected = T.runtimeClass.getName
          IO[Throwable](fail(
            s"Outcome error '$obtained' is not a subtype of '$expected'",
            new Clues(new Clue("thrown", e, e.getClass.getTypeName) :: clues.values)
          ))
      }
  }

def assertCanceledOutcome[F[_], A](outcome: Option[Outcome[F, Throwable, A]],
                                   clues: Clues = new Clues(Nil)
                                  )(implicit loc: Location): IO[Unit] =
  outcome match {
    case None => IO[Unit](fail("Outcome did not contain a value", clues))
    case Some(Outcome.Canceled()) => IO.unit
    case Some(Outcome.Succeeded(fa)) =>
      IO[Unit](fail(
        "Outcome was success instead of cancellation",
        // This should be OK because `F` will usually be cats.Id
        new Clues(new Clue("returned", fa, fa.getClass.getTypeName) :: clues.values)
      ))
    case Some(Outcome.Errored(e)) =>
      e match {
        case _: munit.FailExceptionLike[_] => IO.raiseError(e)
        case _ =>
          IO[Unit](fail(
            "Outcome was error instead of cancellation",
            new Clues(new Clue("thrown", e, e.getClass.getTypeName) :: clues.values)
          ))
      }
  }

def assertSucceededOutcome[F[_], A](outcome: Option[Outcome[F, Throwable, A]],
                                    clues: Clues = new Clues(Nil)
                                   )(implicit loc: Location): IO[F[A]] =
  outcome match {
    case None => IO[F[A]](fail("Outcome did not contain a value", clues))
    case Some(Outcome.Succeeded(fa)) => fa.pure[IO]
    case Some(Outcome.Errored(e)) =>
      e match {
        case _: munit.FailExceptionLike[_] => IO.raiseError(e)
        case _ =>
          IO[F[A]](fail(
            "Outcome was error instead of success",
            new Clues(new Clue("thrown", e, e.getClass.getTypeName) :: clues.values)
          ))
      }
    case Some(Outcome.Canceled()) => IO[F[A]](fail("Outcome was cancellation instead of success", clues))
  }

The examples would then simplify to this:

test("helpers") {
  val test =
    for {
      start <- IO.realTimeInstant
      _ <- IO.sleep(5.seconds)
      _ <- IO.realTimeInstant.assertEquals(start.plusSeconds(5))
    } yield 5

  TestControl.execute(test)
    .flatMap { control =>
      control.tickFor(6.seconds) *> control.results
    }
    .assertSucceededOutcome
    .assertEquals(5)
}

[dharmendra-byte]

Hi,I hope you’re well. I’ve reviewed this issue and would like to request assignment. I’m ready to contribute and will follow the project’s guidelines and standards. Could you please assign this issue to me?

Thanks for your consideration. 🙏
@morgen-peschke