How to test client-side Akka HTTP

Question

I\'ve just started testing out the Akka HTTP Request-Level Client-Side API (Future-Based). One thing I\'ve been struggling to figure out is how to write a unit test for this. Is

Answer 1

Considering that you indeed want to write a unit test for your HTTP client you should pretend there is no real server and not cross the network boundary, otherwise you will obviously do integration tests. A long known recipe of enforcing a unit-testable separation in such cases as yours is to split interface and implementation. Just define an interface abstracting access to an external HTTP server and its real and fake implementations as in the following sketch

import akka.actor.Actor
import akka.pattern.pipe
import akka.http.scaladsl.HttpExt
import akka.http.scaladsl.model.{HttpRequest, HttpResponse, StatusCodes}
import scala.concurrent.Future

trait HTTPServer {
  def sendRequest: Future[HttpResponse]
}

class FakeServer extends HTTPServer {
  override def sendRequest: Future[HttpResponse] =
    Future.successful(HttpResponse(StatusCodes.OK))
}

class RealServer extends HTTPServer {

  def http: HttpExt = ??? //can be passed as a constructor parameter for example

  override def sendRequest: Future[HttpResponse] =
    http.singleRequest(HttpRequest(???))
}

class HTTPClientActor(httpServer: HTTPServer) extends Actor {

  override def preStart(): Unit = {
    import context.dispatcher
    httpServer.sendRequest pipeTo self
  }

  override def receive: Receive = ???
}

and test your HTTPClientActor in conjunction with FakeServer.