Live

The Live trait provides access to the live environment from within the test environment for effects such as printing test results to the console or timing out tests where it is necessary to access the real environment.

Providing Live Environment

To the Entire Effect

The easiest way to access the live environment is to use the live method with an effect that would otherwise access the test environment.

For example, within the test environment, when we use the Clock.currentTime function, it will not execute the live version of the Clock service, rather, it will run the test version of the Clock, which is instantiated with zero-state by default. Thus, the Clock.currentTime will return a 0L value:

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

test("running clock methods in a test environment") {
  assertZIO(Clock.currentTime(TimeUnit.MILLISECONDS))(equalTo(0L)) 
}

To run the Clock.currentTime within the live environment, we should use the Live.live method:

import zio._
import zio.test.{test, _}
import zio.test.Assertion._

import java.util.concurrent.TimeUnit

test("live can access real environment") {
  for {
    live <- Live.live(Clock.currentTime(TimeUnit.MILLISECONDS))
  } yield assertTrue(live != 0L)
}

To the Part of an Effect

The withLive method can be used to apply a transformation to an effect with the live environment while ensuring that the effect itself still runs with the test environment.

For example, assume we have a long-running task that is required to run within the test environment, and we want to timeout it before the assertion. To do this, we should run the timeout operation within the live environment:

import zio._
import zio.test.{test, _}
import zio.test.Assertion._

val longRunningSUT =
  ZIO.attemptBlockingInterrupt {
    // ... 
    Thread.sleep(10000) // simulating a long-running blocking operation
    // ...
  }
  
test("withLive provides real environment to a single part of an effect") {
  assertZIO(Live.withLive(longRunningSUT)(_.timeout(3.seconds)))(anything)
}