How to test the console output of a function or method ? / published by https://github.com/dacr/code-examples-manager #017f95ea-2451-47b1-ac4d-085a0097d59a/ac916f9059e7a470267fc0ee713ea98d6eed2943

testing-stdout.sc

// summary : How to test the console output of a function or method ?
// keywords : scala, scalatest, @testable
// publish : gist
// authors : David Crosson
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2)
// id : 017f95ea-2451-47b1-ac4d-085a0097d59a
// created-on : 2020-05-31T19:54:52Z
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// ---------------------
//> using scala  "3.1.1"
//> using dep "org.scalatest::scalatest:3.2.10"
// ---------------------

import org.scalatest._, flatspec._, matchers._

// -----------------------------------------------
// How to test this kind of border side effect

def printMessage(msg:String):Unit = {
  println(msg)
}

// -----------------------------------------------
// Just by replacing the console by a custom one !

object ThatSpec extends AnyFlatSpec with should.Matchers {
  override def suiteName="ThatSpec"

  "printMessage" should "print a message on the console" in {
    val out = new java.io.ByteArrayOutputStream()
    Console.withOut(out) {
      printMessage("Hello")
    }
    out.toString shouldBe "Hello\n"

  }
}

ThatSpec.execute()