Sunday 17 November 2013

Using Mockito's ArgumentCaptor in Scala

I've been doing what an old colleague of mine used to call "Stack-Whoring" a bit recently - trying to get a few more badges and also up my general reputation on Stack Overflow. It's been fun and educational, and I wanted to post (mainly for my own reference) how to use Mockito's powerful ArgumentCaptor facility from inside a Specs2 example:

I'm just going to nab my own answer from the relevant SO question:
class ApplicationSpec extends Specification with Mockito {

  val mockedNewsRenderer = mock[List[String] => Html]

  val controller = new ApplicationController {
    override def renderNews(s:List[String]) = mockedNewsRenderer(s)

  "Application News Controller" should {

    "Pass a non-empty list of news items to the template" in {
      val result = controller.newsAction(FakeRequest())

      status(result) must beEqualTo(200)

      val captor = ArgumentCaptor.forClass(classOf[List[String]])

      there was one(mockedNewsRenderer).apply(captor.capture())
      val theArgument = captor.getValue
      theArgument.isEmpty must beFalse
The trickiest bit (if you're already familiar with ArgumentCaptor usage in Java) is the use of classOf[T] to get the Scala equivalent of Java's .class so you can then call ArgumentCaptor.forClass().

There's probably scope there for a Pimp My Library tweak to tidy up that particular line - I'm thinking I'd like to just be able to say:
  val captor = ArgumentCaptor.for[List[String]]

Stay tuned ...

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