Mock networking API to produce errors

net.scala

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.util.Random

object NetworkException extends Throwable

def networkRequest(): Future[String] = {
  // let's assume a high rate of failure to make our examples
  // more interesting
  if ((Random.nextFloat * 100) < 80)
    Future.failed(NetworkException)
  else
    Future.successful("<data>")
}