How can I fix the missing implicit value for parameter ta: TildeArrow in a test spec

Question

I\'m working on a simple test spec using spray and I can\'t get it to compile correctly, don\'t know if I\'m doing anything wrong. My version of scala is 2.9.3 and spray 1.0

Answer 1

for akka http:

in my case which refer to akka-http-microservice

• the implicit modifier of executionContext and also need to be removed
• and should reorder the trait like this : class ServiceSpec extends FlatSpec with Matchers with Service with ScalatestRouteTest

Answer 2

The ScalatestRouteTest already provides an implicit ActorySystem. Remove the "implicit" modifier from your actorRefFactory method and the test should get executed.

Spray.io: Can't compile test spec

Answer 3

I can reproduce the precise same error message with Scala 2.10 if myRoutes is not actually a route but a Directive[HNil].

I am therefore guessing that in your unshown service.MyProxy class your route does not complete.

ie

trait MyProxy extends HttpService {
   val myRoutes = path("foo") 
}

Gives this error

trait MyProxy extends HttpService {
  val myRoutes = path("foo") {
   complete(StatusCodes.Accepted)
 }
}

Does not.

Answer 4

To expand a bit on previous answers given, there are some implicits which shouldn't be declared by any other Trait or class that is extends by your Test Class :

• the ActorSystem
• the ExecutionContext
• the DefaultHostInfo (package akka.http.scaladsl.testkit)
• the ActorMaterializer

if any of these is declared elsewhere than in ScalatestRouteTest, you'll have the following error thrown :

could not find implicit value for parameter ...TildeArrow[RequestContext, SomethingHereOther]

Answer 5

I just struggled with this problem. To figure it out, I waded through the Akka HTTP codebase, which is a jungle of implicits.

My problem seemed to be that without the right secondary implicit in place, the correct TildeArrow instance wasn't being found. If you look at the code, the TildeArrow instance, which is required in the error message, is defined as an implicit def injectIntoRoute in the companion object and it requires a whole host of other implicits.

I suggest writing out your code without any of the implicit sugar. This should better help the compiler give you a proper error message:

"MyProxy" should {
  "return a json for GET requests to the /api/getclass/classCode path for a regular request" in {
    val request = Get("/api/getclass/123/")
    val requestWithRoutes = request.~>(myRoutes)(TildeArrow.injectIntoRoute)
    requestWithRoutes.~>(check {
      responseAs[String] must contain("classCode")
      contentType === ContentTypes.`application/json`
    })
  }
}

I think the reason is that since there's no concrete instance of the implicit available, the compiler is trying to satisfy the implicit resolution with the abstract class TildeArrow, and the completely unspecified abstract type, ta.Out, doesn't have a ~> defined.

In my specific case, I was missing an implicit ExecutionContextExecutor, whatever that means.

---

UPDATE

Actually, I looked into it further and the problem was that I had an implicit def ec: ExecutionContextExecutor declared in my route trait, but trait RouteTest defines its name as executor, and so when I defined my own to fulfill the missing implicit, I ended up with two of the same implicit.

It's a cute API, but the implicit magic is way out of control, IMO, especially given how cryptic the error messages tend to be.

Answer 6

In my case, the not found implicit error appeared when in my TestCase I also imported import monix.execution.Scheduler.Implicits.global (which is probably having some sort of ExecutionContext).

I fixed it adding the monix scheduler import just in the method where I needed it, not on the top imports.