Derivation of ZIO Test Generators

Introduction

ZIO Test supports property-based testing via the Gen type. Gen[R, A] is a random generator of values of type A. Such a generator can be used to produce test cases for a property, which can then be checked for validity. The zio-schema-zio-test module provides a way to derive a Gen[R, A] from a Schema[A]. In this section, we will see how this functionality works.

Installation

In order to derive a generator from a ZIO Schema, we need to add the following dependency to our build.sbt file:

libraryDependencies += "dev.zio" %% "zio-schema-zio-test" % 1.7.5

DriveGen

The DriveGen inside zio.schema package provides the gen operator which takes a Schema[A] implicitly and returns a Gen[Sized, A]:

object DeriveGen {
  def gen[A](implicit schema: Schema[A]): Gen[Sized, A] = ???
}

Example

In the following example, we will derive a generator for the Person class using the DeriveGen.gen operator:

import zio.schema.{DeriveGen, DeriveSchema, Schema}
import zio.test.{Gen, Sized}

case class Person(name: String, age: Int)

object Person {
  implicit val schema: Schema[Person] = DeriveSchema.gen
  val gen: Gen[Sized, Person]         = DeriveGen.gen
}

import zio.test._

object ExampleSpec extends ZIOSpecDefault {
  def spec =
    test("example test") {
      check(Person.gen) { p =>
        assertTrue(???)
      }
    }
}