如何模拟 Scala 单例对象？

Question

我正在尝试模拟一个 Scala 单例对象。特别是，我需要模拟在服务组件（被测类）中使用的对象play.api.libs.ws.WS。 使用 Mockito 这是不可能的，测试执行会以下列方式失败：

[error]    MockitoException: : 
[error] Cannot mock/spy class play.api.libs.ws.WS$
[error] Mockito cannot mock/spy following:
[error]   - final classes
[error]   - anonymous classes
[error]   - primitive types  (GeolocationSpec.scala:18)

阅读here，Scalamock 似乎允许这样做：

要模拟一个独立的单例对象，请使用 org.scalamock.annotation.mockObject.

我的服务组件是这样的：

trait GeolocationService {
  def wsClient = WS
  def getPath(origin: Location, destination: Location): Future[Route]
}

class DefaultGeolocationService extends GeolocationService {

  val serviceProviderEndpoint = Play.current.configuration.getString("api.directions.endpoint")

  override def getPath(origin: Location, destination: Location): Future[Route] = {

    val params = Seq(
      "origin" -> s"${origin.lat},${origin.lon}",
      "destination" -> s"${destination.lat},${destination.lon}"
    );
    val resp = wsClient.url(serviceProviderEndpoint.get).withQueryString(params: _*).get()
    resp.map {
      // omitted code
    }
  }
}

我的 build.sbt 有所有这些依赖项：

[...]
"org.scalatest" %% "scalatest" % "2.2.1",
"org.specs2" %% "specs2" % "2.3.13" % "test",
"org.scalamock" %% "scalamock-specs2-support" % "3.0.1" % "test",
"org.scalamock" %% "scalamock-scalatest-support" % "3.0.1" % "test",
"org.scalamock" %% "scalamock" % "3.0.1",
[...]

但我找不到这个：org.scalamock.annotation.mockObject

也许这也可以使用 EasyMock 和 PowerMock 来完成，但我找不到任何 Scala 示例代码。

有什么想法吗？

Answer 1

使用 ScalaMock 3 模拟单例对象不可能，但 Paul Butcher 希望在 ScalaMock 4 中重新引入此功能（请参阅 http://paulbutcher.com/2014/04/15/scalamock-status-report/）

Answer 2

不要嘲笑单身人士。代替 WS，让您的服务组件依赖于隐藏它的瘦外观：

trait GeolocationService {
  def ws: (String, Seq[String]) => Promise[Response] = { (url, params) =>
    wsClient.url(serviceProviderEndpoint.get).withQueryString(params: _*).get()
  }
  def getPath(origin: Location, destination: Location): Future[Route]
}

在您的测试中，只需用一个 mock 覆盖 ws 方法，现在很容易创建：

val mockedWs = mock[(String, Seq[String]) => Promise[Response]]
// TODO specify mock's behavior here
val service = new DefaultGeolocationService() {
  override def ws = mockedWs
}

Answer 3

我不喜欢改变设计来适应这种限制。基本上我能得到的都是改变设计然后使用mock框架

  //since mocking frameworks on SCALA is not support mocking singleton
  //hacks are either required to change the design or ...
  //I'd rather putting the mocking logic here by myself
  var testUser:Option[User] = None;

  def getCurrentUser(request: Request[Object]) = {
    if( testUser != None ){
    testUser;
  }

希望对你有帮助。

Answer 4

为什么不使用蛋糕图案？

这有点冗长，但它会解决你的模拟问题。

trait GeolocationServiceComponent {
   val geolocationService:GeolocationService
   trait GeolocationService {      
      def wsClient
      def getPath(origin:Location, destination: Location): Future[Route]   
   }
}

trait GeolocationServiceComponentImpl {
   val geolocationService = new GeolocationService {
      override def wsClient = WS
   }
}


class DefaultGeolocationService extends GeolocationServiceComponent ...

//Defined into your test class
trait MockGeolocationServiceComponent {
       val geolocationService = Mock[GeolocationService]
//Here you define your mock logic       
}

你也可以使用 monads 来做到这一点，但我从来没有实现过，这里有描述： Scala dependency injection: alternatives to implicit parameters