controller.scala

package com.twitter.demo

import com.twitter.macaw.{FinatraController, Status}

class EchoController extends  FinatraController {

  get("/echo.json") { request =>
    request.params.get("s") match {
      case Some(s) =>
        actionJsonObjectResponse(Map("echo" -> s))
      case None =>
        actionApiError("missing parameter: s", Status.BadRequest)
    }
  }

}

spec.scala

package com.twitter.demo

import com.twitter.macaw.test.MacawSpec
import com.twitter.macaw.Status

import org.junit.runner.RunWith
import org.scalatest.junit.JUnitRunner

@RunWith(classOf[JUnitRunner])
class EchoControllerSpec extends MacawSpec {

  def app = { new EchoController() }

  "GET /echo.json?s=foo" should "respond with an echo" in {
    get("/echo.json", Map("s"->"foo"))
    response should matchActionResponse(Map("echo" -> "foo"))
  }

  "GET /echo.json" should "respond with an error" in {
    get("/echo.json")
    response should matchActionApiError("missing parameter: s", Status.BadRequest)
  }

}