Akka gRPC Quickstart with Scala

Testing gRPC

The tests in the Hello World example illustrates use of the ScalaTest framework. The test coverage is not complete. It only shows how to get started with testing gRPC services. You could add to it as an exercise to increase your own knowledge.

Let’s look at the test class definition in the GreeterSpec.scala source file:

copysourcepackage com.example.helloworld

import akka.actor.testkit.typed.scaladsl.ActorTestKit
import akka.actor.typed.ActorSystem
import akka.actor.typed.scaladsl.Behaviors
import akka.grpc.GrpcClientSettings

import com.typesafe.config.ConfigFactory

import org.scalatest.BeforeAndAfterAll
import org.scalatest.concurrent.ScalaFutures
import org.scalatest.matchers.should.Matchers
import org.scalatest.wordspec.AnyWordSpec

import scala.concurrent.duration._

class GreeterSpec
  extends AnyWordSpec
  with BeforeAndAfterAll
  with Matchers
  with ScalaFutures {

  implicit val patience: PatienceConfig = PatienceConfig(scaled(5.seconds), scaled(100.millis))

  // important to enable HTTP/2 in server ActorSystem's config
  val conf = ConfigFactory.parseString("akka.http.server.enable-http2 = on")
    .withFallback(ConfigFactory.defaultApplication())

  val testKit = ActorTestKit(conf)

  val serverSystem: ActorSystem[_] = testKit.system
  val bound = new GreeterServer(serverSystem).run()

  // make sure server is bound before using client
  bound.futureValue

  implicit val clientSystem: ActorSystem[_] = ActorSystem(Behaviors.empty, "GreeterClient")

  val client =
    GreeterServiceClient(GrpcClientSettings.fromConfig("helloworld.GreeterService"))

  override def afterAll(): Unit = {
    ActorTestKit.shutdown(clientSystem)
    testKit.shutdownTestKit()
  }

  "GreeterService" should {
    "reply to single request" in {
      val reply = client.sayHello(HelloRequest("Alice"))
      reply.futureValue should ===(HelloReply("Hello, Alice"))
    }
  }
}

Note how we create two ActorSystems, one for the server and another for the client. The test is then using the client to verify that it retrieves the expected responses from the server.

Unit testing

The above test example is a full integration test using real client and server, including communication via HTTP/2. For some testing of the service implementation it might be more appropriate to write unit tests without interaction via the gRPC client. Since the service interface and implementation doesn’t require any gRPC infrastructure it can be tested without binding it to a HTTP server.

copysourcepackage com.example.helloworld

import akka.actor.testkit.typed.scaladsl.ActorTestKit
import akka.actor.typed.ActorSystem

import org.scalatest.BeforeAndAfterAll
import org.scalatest.concurrent.ScalaFutures
import org.scalatest.matchers.should.Matchers
import org.scalatest.wordspec.AnyWordSpec

import scala.concurrent.duration._

class GreeterServiceImplSpec
  extends AnyWordSpec
  with BeforeAndAfterAll
  with Matchers
  with ScalaFutures {

  val testKit = ActorTestKit()

  implicit val patience: PatienceConfig = PatienceConfig(scaled(5.seconds), scaled(100.millis))

  implicit val system: ActorSystem[_] = testKit.system

  val service = new GreeterServiceImpl(system)

  override def afterAll(): Unit = {
    testKit.shutdownTestKit()
  }

  "GreeterServiceImpl" should {
    "reply to single request" in {
      val reply = service.sayHello(HelloRequest("Bob"))
      reply.futureValue should ===(HelloReply("Hello, Bob"))
    }
  }
}

Add streaming tests

As an exercise to increase your understanding you could add tests for the streaming call, both as integration test and unit test style.

The Akka documentation of Testing streams might be useful.