util

Type Members

1. final class TestContext extends ExecutionContext

   

   A scala.concurrent.ExecutionContext implementation and a provider of cats.effect.Timer instances, that can simulate async boundaries and time passage, useful for testing purposes.

   A scala.concurrent.ExecutionContext implementation and a provider of cats.effect.Timer instances, that can simulate async boundaries and time passage, useful for testing purposes.

   Usage for simulating an ExecutionContext):

   implicit val ec = TestContext()
   
   ec.execute(new Runnable { def run() = println("task1") })
   
   ex.execute(new Runnable {
     def run() = {
       println("outer")
   
       ec.execute(new Runnable {
         def run() = println("inner")
       })
     }
   })
   
   // Nothing executes until `tick` gets called
   ec.tick()
   
   // Testing the resulting state
   assert(ec.state.tasks.isEmpty)
   assert(ec.state.lastReportedFailure == None)

   Our TestContext can also simulate time passage, as we are able to builds a cats.effect.Timer instance for any data type that has a LiftIO instance:

   val ctx = TestContext()
   
   val timer: Timer[IO] = ctx.timer[IO]

   We can now simulate actual time:

   val io = timer.sleep(10.seconds) *> IO(1 + 1)
   val f = io.unsafeToFuture()
   
   // This invariant holds true, because our IO is async
   assert(f.value == None)
   
   // Not yet completed, because this does not simulate time passing:
   ctx.tick()
   assert(f.value == None)
   
   // Simulating time passing:
   ctx.tick(10.seconds)
   assert(f.value == Some(Success(2))

   Simulating time makes this pretty useful for testing race conditions:

   val never = IO.async[Int](_ => {})
   val timeoutError = new TimeoutException
   val timeout = timer.sleep(10.seconds) *> IO.raiseError[Int](timeoutError)
   
   val pair = (never, timeout).parMapN(_ + _)
   
   // Not yet
   ctx.tick()
   assert(f.value == None)
   // Not yet
   ctx.tick(5.seconds)
   assert(f.value == None)
   
   // Good to go:
   ctx.tick(5.seconds)
   assert(f.value, Some(Failure(timeoutError)))

2. trait TestInstances extends AnyRef

   

   Defines instances for Future and for IO, meant for law testing by means of TestContext.

   Defines instances for Future and for IO, meant for law testing by means of TestContext.

   The TestContext interpreter is used here for simulating asynchronous execution.