TestClock

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.duration._
 import zio.test.environment.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.duration._
 import zio.test.environment.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.

trait Serializable

class Object

trait Matchable

class Any

TestClock.type

Type members

Classlikes

Data represents the state of the TestClock, including the clock time and time zone.

Sleep represents the state of a scheduled effect, including the time the effect is scheduled to run, a promise that can be completed to resume execution of the effect, and the fiber executing the effect.

Companion:: object

Companion:: class

WarningData describes the state of the warning message that is displayed if a test is using time by is not advancing the TestClock. The possible states are Start if a test has not used time, Pending if a test has used time but has not adjusted the TestClock, and Done if a test has adjusted the TestClock or the warning message has already been displayed.

Companion:: object

Companion:: class

Value members

Concrete methods

Accesses a TestClock instance in the environment and increments the time by the specified duration, running any actions scheduled for on or before the new time in order.

Constructs a new Test object that implements the TestClock interface. This can be useful for mixing in with implementations of other interfaces.

Accesses a TestClock instance in the environment and sets the clock time to the specified OffsetDateTime, running any actions scheduled for on or before the new time in order.

Accesses a TestClock instance in the environment and sets the clock time to the specified time in terms of duration since the epoch, running any actions scheduled for on or before the new time in order.

Accesses a TestClock instance in the environment, setting the time zone to the specified time zone. The clock time in terms of nanoseconds since the epoch will not be altered and no scheduled actions will be run as a result of this effect.

Concrete fields

Accesses a TestClock instance in the environment and saves the clock state in an effect which, when run, will restore the TestClock to the saved state.

Accesses a TestClock instance in the environment and returns a list of times that effects are scheduled to run.

Accesses a TestClock instance in the environment and returns the current time zone.