I'm working on a Scala url shortener (to be hosted at my awesomely problem-causing ❺➠.ws domain). Since this is such a small application, I'm rolling it ground-up from the Servlet spec only, to get a feel for Scala without having to worry about a lot of dependencies. As such, one of the things I need to do is parse the requestor's "representation", i.e. determine if I'm serving JSON, XML, or HTML. Since this comes from the Accept: header, my tests will need to mock HttpServletRequest. 

val enumeration = createMock(
    classOf[java.util.Enumeration[String]])

expect(enumeration.hasMoreElements).andReturn(true)
expect(enumeration.nextElement).andReturn("TEXT/HTML")
expect(enumeration.hasMoreElements).andReturn(false)
// the following call doesn't compile!!!
expect(request.getHeaders(parser.ACCEPT_HEADER))
  .andReturn(enumeration)
expect(request.getParameter(parser.TYPE_PARAM))
  .andReturn(null)

replay(request)
replay(enumeration)

val t = parser.determineRepresentation(request)
t should equal (Some("text/html"))
When I compile this test, I get the following baffling error message: 
TestRepresentationParser.scala:21: type mismatch;
found   : java.util.Enumeration[String]
required: java.util.Enumeration[?0] where type ?0
    EasyMock.expect(request.getHeaders(parser.ACCEPT_HEADER))
        .andReturn(enumeration)
Um, OK? I tried zillions of ways to cast things, even creating my own implementation of Enumeration[String], to no avail. There seems to be some problem with the fact that HttpServletRequest returns a non-parameterized Enumeration in its interface, but Scala won't let me create such a thing.

I had given up on testing this for a while, but eventually the simple solution prevailed: 

EasyMock.expect(request.getHeaders(parser.ACCEPT_HEADER))
// this call is obviously not type-checked, so it works
expectLastCall.andReturn(enumeration)
Kinda cheesy, and I kinda feel stupid for not thinking of it sooner.