TestClock

trait TestClock extends Clock with Restorable

TestClock makes it easy to deterministically and efficiently test effects involving the passage of time.

Instead of waiting for actual time to pass, sleep and methods implemented in terms of it schedule effects to take place at a given clock time. Users can adjust the clock time using the adjust and setTime methods, and all effects scheduled to take place on or before that time will automatically be run in order.

For example, here is how we can test ZIO#timeout using TestClock:

 import zio.ZIO
 import zio.test.TestClock

 for {
   fiber  <- ZIO.sleep(5.minutes).timeout(1.minute).fork
   _      <- TestClock.adjust(1.minute)
   result <- fiber.join
 } yield result == None

Note how we forked the fiber that sleep was invoked on. Calls to sleep and methods derived from it will semantically block until the time is set to on or after the time they are scheduled to run. If we didn't fork the fiber on which we called sleep we would never get to set the time on the line below. Thus, a useful pattern when using TestClock is to fork the effect being tested, then adjust the clock time, and finally verify that the expected effects have been performed.

For example, here is how we can test an effect that recurs with a fixed delay:

 import zio.Queue
 import zio.test.TestClock

 for {
   q <- Queue.unbounded[Unit]
   _ <- q.offer(()).delay(60.minutes).forever.fork
   a <- q.poll.map(_.isEmpty)
   _ <- TestClock.adjust(60.minutes)
   b <- q.take.as(true)
   c <- q.poll.map(_.isEmpty)
   _ <- TestClock.adjust(60.minutes)
   d <- q.take.as(true)
   e <- q.poll.map(_.isEmpty)
 } yield a && b && c && d && e

Here we verify that no effect is performed before the recurrence period, that an effect is performed after the recurrence period, and that the effect is performed exactly once. The key thing to note here is that after each recurrence the next recurrence is scheduled to occur at the appropriate time in the future, so when we adjust the clock by 60 minutes exactly one value is placed in the queue, and when we adjust the clock by another 60 minutes exactly one more value is placed in the queue.

Companion:
object
trait Clock
class Object
trait Matchable
class Any
class Test

Value members

Abstract methods

def adjust(duration: Duration)(implicit trace: Trace): UIO[Unit]
def adjustWith[R, E, A](duration: Duration)(zio: ZIO[R, E, A])(implicit trace: Trace): ZIO[R, E, A]
def setTime(instant: Instant)(implicit trace: Trace): UIO[Unit]
def setTimeZone(zone: ZoneId)(implicit trace: Trace): UIO[Unit]
def sleeps(implicit trace: Trace): UIO[List[Instant]]
def timeZone(implicit trace: Trace): UIO[ZoneId]

Inherited methods

def currentDateTime(implicit trace: Trace): UIO[OffsetDateTime]
Inherited from:
Clock
def currentTime(unit: => ChronoUnit)(implicit trace: Trace, d: DummyImplicit): UIO[Long]
Inherited from:
Clock
def currentTime(unit: => TimeUnit)(implicit trace: Trace): UIO[Long]
Inherited from:
Clock
def instant(implicit trace: Trace): UIO[Instant]
Inherited from:
Clock
def javaClock(implicit trace: Trace): UIO[Clock]
Inherited from:
Clock
def localDateTime(implicit trace: Trace): UIO[LocalDateTime]
Inherited from:
Clock
def nanoTime(implicit trace: Trace): UIO[Long]
Inherited from:
Clock
def save(implicit trace: Trace): UIO[UIO[Unit]]
Inherited from:
Restorable
def scheduler(implicit trace: Trace): UIO[Scheduler]
Inherited from:
Clock
def sleep(duration: => Duration)(implicit trace: Trace): UIO[Unit]
Inherited from:
Clock