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

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.