Restoring State of Test Services

ZIO Test has some test aspects which restore the state of given restorable test services, such as TestClock, TestConsole, TestRandom and TestSystem, to their starting state after the test is run. Note that these test aspects are only useful when we are repeating tests.

Here is a list of restore methods:

• TestAspect.restore
• TestAspect.restoreTestClock
• TestAspect.restoreTestConsole
• TestAspect.restoreTestRandom
• TestAspect.restoreTestSystem
• TestAspect.restoreTestEnvironment

Let's try an example. Assume we have written the following test aspect, which repeats the test 5 times:

When we run a test with this testing aspect, on each try, we have a polluted test environment:

import zio._
import zio.test.{ test, _ }
import java.util.concurrent.TimeUnit

suite("clock suite")(
  test("adjusting clock") {
    for {
      clock <- ZIO.clock
      _     <- TestClock.adjust(1.second)
      time  <- clock.currentTime(TimeUnit.SECONDS).debug("current time")
    } yield assertTrue(time == 1)
  } @@ repeat5
)

This test fails in the second retry:

current time: 1
current time: 2
- some suite
  - clock suite
    - adjusting clock
      ✗ 2 was not equal to 1
      time == 1
      time = 2

It failed because of the first run of the test changed the state of the TestClock service, so on the next run, the initial state of the test is not zero. In such a situation, when we are repeating a test, after each run we can restore the state of the test to its initial state, using TestAspect.restore* test aspects:

import zio._
import zio.test.{ test, _ }
import java.util.concurrent.TimeUnit

suite("clock suite")(
  test("adjusting clock") {
    for {
      clock <- ZIO.clock
      _     <- TestClock.adjust(1.second)
      time  <- clock.currentTime(TimeUnit.SECONDS).debug("current time")
    } yield assertTrue(time == 1)
  } @@ TestAspect.restoreTestClock @@ repeat5
)

The output of running this test would be as follows:

current time: 1
current time: 1
current time: 1
current time: 1
current time: 1
current time: 1
+ clock suite
  + adjusting clock
  Ran 1 test in 470 ms: 1 succeeded, 0 ignored, 0 failed