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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.

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)))
Self Type
TestContext
Source
TestContext.scala
Linear Supertypes
ExecutionContext, AnyRef, Any
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  1. TestContext
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Visibility
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Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##: Int
    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  4. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  5. def clone(): AnyRef
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.CloneNotSupportedException]) @native()
  6. def contextShift[F[_]](implicit F: Async[F]): ContextShift[F]

    Derives a cats.effect.ContextShift from this TestContext, for any data type that has an Async instance.

    Derives a cats.effect.ContextShift from this TestContext, for any data type that has an Async instance.

    Example:

    val ctx = TestContext()
// Building a Timer[IO] from this:
implicit val timer: Timer[IO] = ctx.timer[IO]

// Can now simulate 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))
  7. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  8. def equals(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef → Any
  9. def execute(r: Runnable): Unit

    Inherited from ExecutionContext, schedules a runnable for execution.

    Inherited from ExecutionContext, schedules a runnable for execution.

    Definition Classes
    TestContext → ExecutionContext
  10. def finalize(): Unit
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.Throwable])
  11. final def getClass(): Class[_ <: AnyRef]
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  12. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  13. def ioContextShift: ContextShift[IO]

    Derives a cats.effect.ContextShift from this TestContext for IO.

  14. def ioTimer: Timer[IO]

    Derives a cats.effect.Timer from this TestContext for IO.

  15. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  16. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  17. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  18. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  19. def reportFailure(cause: Throwable): Unit

    Inherited from ExecutionContext, reports uncaught errors.

    Inherited from ExecutionContext, reports uncaught errors.

    Definition Classes
    TestContext → ExecutionContext
  20. def state: State

    Returns the internal state of the TestContext, useful for testing that certain execution conditions have been met.

  21. final def synchronized[T0](arg0: => T0): T0
    Definition Classes
    AnyRef
  22. def tick(time: FiniteDuration = Duration.Zero): Unit

    Triggers execution by going through the queue of scheduled tasks and executing them all, until no tasks remain in the queue to execute.

    Triggers execution by going through the queue of scheduled tasks and executing them all, until no tasks remain in the queue to execute.

    Order of execution isn't guaranteed, the queued Runnables are being shuffled in order to simulate the needed non-determinism that happens with multi-threading.

    implicit val ec = TestContext()

val f = Future(1 + 1).flatMap(_ + 1)
// Execution is momentarily suspended in TestContext
assert(f.value == None)

// Simulating async execution:
ec.tick()
assert(f.value, Some(Success(2)))

    The optional parameter can be used for simulating time, to be used in combination with cats.effect.Timer. See the timer method.

    Example:

    val ctx = TestContext()
// Building a Timer[IO] from this:
implicit val timer: Timer[IO] = ctx.timer[IO]

// Can now simulate 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))
    time

    is an optional parameter for simulating time passing;

  23. def tickOne(): Boolean

    Executes just one tick, one task, from the internal queue, useful for testing that a some runnable will definitely be executed next.

    Executes just one tick, one task, from the internal queue, useful for testing that a some runnable will definitely be executed next.

    Returns a boolean indicating that tasks were available and that the head of the queue has been executed, so normally you have this equivalence:

    while (ec.tickOne()) {}
// ... is equivalent with:
ec.tick()

    Note that ask extraction has a random factor, the behavior being like tick, in order to simulate non-determinism. So you can't rely on some ordering of execution if multiple tasks are waiting execution.

    returns

    true if a task was available in the internal queue, and was executed, or false otherwise

  24. def timer[F[_]](implicit F: LiftIO[F]): Timer[F]

    Derives a cats.effect.Timer from this TestContext, for any data type that has a LiftIO instance.

    Derives a cats.effect.Timer from this TestContext, for any data type that has a LiftIO instance.

    Example:

    val ctx = TestContext()
// Building a Timer[IO] from this:
implicit val timer: Timer[IO] = ctx.timer[IO]

// Can now simulate 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))
  25. def toString(): String
    Definition Classes
    AnyRef → Any
  26. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException])
  27. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException])
  28. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException]) @native()

Deprecated Value Members

  1. def prepare(): ExecutionContext
    Definition Classes
    ExecutionContext
    Annotations
    @deprecated
    Deprecated

    (Since version 2.12.0) preparation of ExecutionContexts will be removed

Inherited from ExecutionContext

Inherited from AnyRef

Inherited from Any

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