TestContext

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

Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def ##(): Int

Definition Classes
AnyRef → Any
final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def asInstanceOf[T0]: T0

Definition Classes
Any
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )

def contextShift[F[_]](implicit F: Async[F]): ContextShift[F]

Derives a cats.effect.ContextShift from this TestContext, for any data type that has a LiftIO and MonadError 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))

final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef
def equals(arg0: Any): Boolean

Definition Classes
AnyRef → Any
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
def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
final def getClass(): Class[_]

Definition Classes
AnyRef → Any
def hashCode(): Int

Definition Classes
AnyRef → Any
final def isInstanceOf[T0]: Boolean

Definition Classes
Any
final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef
final def notify(): Unit

Definition Classes
AnyRef
final def notifyAll(): Unit

Definition Classes
AnyRef
def prepare(): ExecutionContext

Definition Classes
ExecutionContext
def reportFailure(cause: Throwable): Unit

Inherited from ExecutionContext, reports uncaught errors.
Inherited from ExecutionContext, reports uncaught errors.

Definition Classes
TestContext → ExecutionContext
def state: State

Returns the internal state of the TestContext, useful for testing that certain execution conditions have been met.
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef

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.

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;

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

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.

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))

def toString(): String

Definition Classes
AnyRef → Any
final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )

Related Docs: object TestContext | package util

final class TestContext extends ExecutionContext

Value Members

final def !=(arg0: Any): Boolean

final def ##(): Int

final def ==(arg0: Any): Boolean

final def asInstanceOf[T0]: T0

def clone(): AnyRef

def contextShift[F[_]](implicit F: Async[F]): ContextShift[F]

final def eq(arg0: AnyRef): Boolean

def equals(arg0: Any): Boolean

def execute(r: Runnable): Unit

def finalize(): Unit

final def getClass(): Class[_]

def hashCode(): Int

final def isInstanceOf[T0]: Boolean

final def ne(arg0: AnyRef): Boolean

final def notify(): Unit

final def notifyAll(): Unit

def prepare(): ExecutionContext

def reportFailure(cause: Throwable): Unit

def state: State

final def synchronized[T0](arg0: ⇒ T0): T0

def tick(time: FiniteDuration = Duration.Zero): Unit

def tickOne(): Boolean

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

def toString(): String

final def wait(): Unit

final def wait(arg0: Long, arg1: Int): Unit

final def wait(arg0: Long): Unit

Inherited from ExecutionContext

Inherited from AnyRef

Inherited from Any

Ungrouped