TestControl.scala

//> using scala "3.2.1"
//> using lib "org.typelevel::cats-effect-testkit:3.4.0"
//> using lib "org.typelevel::munit-cats-effect-3:1.0.7"

import cats.effect.*
import cats.effect.testkit.TestControl
import munit.CatsEffectSuite
import scala.concurrent.duration.*

class Suite extends CatsEffectSuite:
  test("basic usage") {
    val run = IO.ref(false).flatMap { ref =>
      val background = IO.sleep(5.seconds) >> ref.set(true)

      background.start >> IO.sleep(10.seconds) >> ref.get.assert
    }

    TestControl.executeEmbed(run)
  }

  test("stepped execution") {
    IO.ref(false).flatMap { ref =>
      val background = IO.sleep(5.seconds) >> ref.set(true)
      val run = background.start >> IO.sleep(10.seconds) >> ref.get.assert

      TestControl.execute(run).flatMap { ctrl =>
        for
          // Schedule initial fibers
          _ <- ctrl.tick
          _ <- ref.get.assertEquals(false)
          // Advance time but do not schedule fibers
          _ <- ctrl.advance(5.seconds)
          _ <- ref.get.assertEquals(false)
          // Now schedule - background fiber should run
          _ <- ctrl.tick
          // Background fiber has now modified the Ref
          _ <- ref.get.assert
          // Run to completion
          _ <- ctrl.tickAll
        yield ()
      }
    }
  }