Set a command line argument for Scalatest with SBT - scala

Question

I'm trying to write an integration test for a small command line app I'm writing with Scala and SBT. My app would usually be run from the SBT prompt like so:
> run "my arg"
The argument "my arg" is accessed in the app with args(0). For an integration test how can I simulate calling run with an argument and asserting console output?

Answer 1

Your app needs to have an object with main method that takes Array[String] as parameter.
It looks like this
object Main extends App {
print("hi, " + args(0))
}
or like this
object Main {
def main(args: Array[String]) = print("hi, " + args(0))
}
Anyway you definitely have this kind of entry point if you can do > run "my arg" in sbt.
It is just an object with a method called main that you can call wherever you want. Just import it and use:
Main.main(Array("my arg"))
that would print the text to the console when executed. We need to redirect the console output to some other stream to be able to verify it.
Using answer from Redirect stdout in another thread you can come up with something like this:
val baos = new ByteArrayOutputStream
val ps = new PrintStream(baos)
Console.withOut(ps)(Main.main(Array("my arg")))
val output = baos.toString
And you can do all sort of tests on output value
You can then create a helper method to handle this for you
def outputFor(args: String*): String = {
val baos = new ByteArrayOutputStream
val ps = new PrintStream(baos)
Console.withOut(ps)(Main.main(args.toArray))
baos.toString
}
And then easly test your app
"My app" should "greet me" {
outputFor("harryg") shouldBe "hi, harryg"
}
Just to clarify, the whole solution has nothing to do with sbt itself, we directly call the program in a similar way that sbt would do it.