Question

Is there something in Scalatest that will allow me to test the output to the standard out via a println statement?

So far I’ve mainly been using FunSuite with ShouldMatchers.

e.g. how do we check the printed output of

object Hi {
  def hello() {
    println("hello world")
  }
}

Answer 1

The usual way to test print statements on the console is to structure your program a bit differently so that you can intercept those statements. You can for example introduce an Output trait:

  trait Output {
    def print(s: String) = Console.println(s)
  }

  class Hi extends Output {
    def hello() = print("hello world")
  }

And in your tests you can define another trait MockOutput actually intercepting the calls:

  trait MockOutput extends Output {
    var messages: Seq[String] = Seq()

    override def print(s: String) = messages = messages :+ s
  }


  val hi = new Hi with MockOutput
  hi.hello()
  hi.messages should contain("hello world")