下面是一个示例代码，演示如何使用Akka Http测试Gzip响应：

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.model._
import akka.http.scaladsl.model.headers._
import akka.stream.ActorMaterializer
import akka.util.ByteString
import scala.concurrent.Await
import scala.concurrent.duration._

object GzipResponseTest extends App {
  implicit val system = ActorSystem()
  implicit val materializer = ActorMaterializer()
  implicit val executionContext = system.dispatcher

  val serverBinding = Http().bindAndHandle(route, "localhost", 8080)

  val request = HttpRequest(uri = "http://localhost:8080")
    .addHeader(AcceptEncoding(HttpEncodings.gzip))

  val responseFuture = Http().singleRequest(request)

  val response = Await.result(responseFuture, 5.seconds)

  response.entity.dataBytes.runFold(ByteString(""))(_ ++ _).foreach { body =>
    val responseBody = body.decodeString("UTF-8")
    println(responseBody)
  }

  serverBinding.flatMap(_.unbind()).onComplete(_ => system.terminate())

  def route = {
    import akka.http.scaladsl.server.Directives._
    import akka.http.scaladsl.server.directives.CachingDirectives._
    import akka.http.scaladsl.server.directives.RouteDirectives._

    path("") {
      get {
        complete {
          val gzipEntity = HttpEntity(ContentTypes.`text/plain(UTF-8)`, "Hello, World!")
            .withHeaders(`Content-Encoding`(HttpEncodings.gzip))

          HttpResponse(entity = gzipEntity)
        }
      }
    }
  }
}

这个示例代码创建了一个简单的Akka Http服务器，该服务器返回一个Gzip压缩的文本响应。然后，它使用Accept-Encoding头发送一个请求，指示客户端接受Gzip编码的响应。最后，它解压缩并打印出响应体的内容。

请确保在构建项目时包含适当的依赖项。例如，在sbt项目中，您需要添加以下依赖项：

libraryDependencies ++= Seq(
  "com.typesafe.akka" %% "akka-http" % "10.2.0",
  "com.typesafe.akka" %% "akka-stream" % "2.6.16"
)

这样，您就可以运行示例代码并测试Gzip响应了。