Mocking Methods for Testing Akka HTTP Routes

In this blog, I am going to explain how to write unit test cases for routes in Akka HTTP.

First and foremost, the test cases should not hit our backend logic — remember that we are only testing our routes, routes basically form the controller layer in our application. They control the request/response cycle. They tell which business logic should respond to the request and send the control to the corresponding business layer logic. We must always follow best coding practices while defining our routes.

So let us understand how to write unit test cases for the routes with the help of an example.

Suppose that we have a simple route which handles a "/adduser" post request:

trait RestService {

  implicit val userFormat = jsonFormat2(User)
  val userImpl: UserImpl

  val route =
    post {
      path("adduser") {
        entity(as[User]) { user =>
          val saved: Future[Done] = userImpl.addUser(user)
          onComplete(saved) { _ =>
            complete("user added")
          }
        }
      }
    } 

}

class RestServiceImpl extends RestService {
  val userImpl = UserImpl
}

Now in this route, user.Impl.add(user) is calling the backend business logic for adding a user to the database, so this method needs to be mocked while testing — otherwise, this method would be called every time we test this route, which is not an ideal scenario for unit testing.

There are many ways to mock this method. I have used Mockito, a mocking framework for unit testing, to mock this method while testing my post route.

Using Mockito is very easy. We just need to import the following library dependency and then write our unit test.

 libraryDependencies += “org.mockito“ % “mockito-all“ % “1.9.5“ % Test 

Now, the unit test case for this post route can be written like this:

class RestSpec extends WordSpec with Matchers with ScalatestRouteTest with MockitoSugar {

  val mockUserImpl = mock[UserImpl]

  object TestObject extends RestService {
    val userImpl = mockUserImpl
  }

  "The service" should {

    "return user added as response for a Post request to /adduser" in {
      when(mockUserImpl.addUser(User(2, "test"))).thenReturn(Future.successful(Done))

      val jsonRequest = ByteString(
        s"""
           |{
           |    "id":2,
           |    "name":"test"
           |}
        """.stripMargin)
      val postRequest = HttpRequest(
        HttpMethods.POST,
        uri = "/adduser",
        entity = HttpEntity(MediaTypes.`application/json`, jsonRequest))

      postRequest ~>  Route.seal(TestObject.route) ~> check {
        status.isSuccess() shouldEqual true
        responseAs[String] shouldEqual "user added"
      }
    }

Firstly, we need to extend ScalaTest's MockitoSugar trait that provides some basic syntax sugar for Mockito.

Then, in this test case, I have mocked the UserImpl object using the Mockito framework. and then the mocked instance is used with the when/then pattern to mock the adduser method.

I am sending the user information in JSON format in the body of post request and finally checking the assertions.

References:

• http://www.scalatest.org/user_guide/testing_with_mock_objects
• http://blog.madhukaraphatak.com/akka-http-testing/
• https://doc.akka.io/docs/akka-http/current/routing-dsl/testkit.html

This article was first published on the Knoldus blog.