Sized

The Sized service enables the Sized Generators to access the size from the ZIO Test environment:

trait Sized extends Serializable {
  def size: UIO[Int]
  def withSize[R, E, A](size: Int)(zio: ZIO[R, E, A]): ZIO[R, E, A]
}

The Sized service has two APIs:

1. Sized.size
2. Sized.withSize

Let's go through each one:

Operations

size

To access the default size value from the environment, we can use the Sized.size API. In ZIO Test, it is used to enable the sized generators access the size from the environment:

object Sized {
  def withSize[R, E, A](size: Int)(zio: ZIO[R, E, A]): ZIO[R, E, A] = ???
}

For example, the Gen.sized generator has the following signature:

object Gen {
  def sized[R, A](f: Int => Gen[R, A]): Gen[R, A] = ???
}

It applies the size to the given function of type Int => Gen[R, A]. We should note that the sized generator obtains the size value from the environment internally.

In the following example, we are creating a sized generator, which generates integer values within the specified range. In this generator, the lower bound is bound to zero, and the upper bound is bound to the size value, which is obtained from the ZIO environment:

import zio._
import zio.test._

val sizedInts: Gen[Any, Int] = 
  Gen.sized(Gen.int(0, _))

To generate some sample values, we can use Gen#runCollectN operator on that:

val samples: UIO[List[Int]] = 
  sizedInts.runCollectN(5).debug

withSize

To change the default size temporarily, we can use the Size.withSize. It takes a size and a ZIO effect, and runs that effect bounded with the given size:

object Sized {
  def withSize[R, E, A](size: Int)(zio: ZIO[R, E, A]): ZIO[R, E, A] = ???
}

import zio._
import zio.test._

val effect     : UIO[String] = ZIO.succeed("effect")
val sizedEffect: UIO[String] = Sized.withSize(10)(effect)

ZIO Test has a test aspect called TestAspect.size which is a helper method for this operation. This test aspect runs each test with the given size value:

import zio._
import zio.test._

object SizedSpec extends ZIOSpecDefault {
  def spec =
    suite("sized") {
      test("bounded int generator shouldn't cross its boundaries") {
        check(Gen.sized(Gen.int(0, _))) { n =>
          assertTrue(n >= 0 && n <= 200)
        }
      } @@ TestAspect.size(200)
    }
}