Writing Our First Test

Any object that implements the ZIOSpecDefault trait is a runnable test. So to start writing tests we need to extend ZIOSpecDefault, which requires a Spec:

import zio.test._

object HelloWorldSpec extends ZIOSpecDefault {
  def spec = 
    suite("HelloWorldSpec")(
      ??? // all tests go here
    )
}

note

In order to have runnable tests, the ZIOSpecDefault trait must be extended by an object that implements the spec method. If we extend this trait in a class, the test runner will not be able to find the tests.

ZIOSpecDefault is very similar in its logic of operations to ZIOAppDefault. Instead of providing one ZIO application at the end of the world, we provide a suite that can be a tree of other suites and tests.

import zio._
import zio.test._
import zio.test.Assertion._

import java.io.IOException

import HelloWorld._

object HelloWorld {
  def sayHello: ZIO[Any, IOException, Unit] =
    Console.printLine("Hello, World!")
}

object HelloWorldSpec extends ZIOSpecDefault {
  def spec = suite("HelloWorldSpec")(
    test("sayHello correctly displays output") {
      for {
        _      <- sayHello
        output <- TestConsole.output
      } yield assertTrue(output == Vector("Hello, World!\n"))
    }
  )
}

In the example above, our test involved the effect of printing to the console, but we didn't have to do anything differently in our test. Also note that the helloWorld method in the above program does not actually print a string to the console instead writes it to a buffer for testing.