Swift function with a closure parameter seen as error type inside Unit Testing Module

I'm trying to write Unit tests for my Article Model. I have added the model as a test target.

I am able to access class functions without closure parameters in it but when I try to use a function with a closure, here's what Xcode's autocompletion gave

The full function prototype of 'fetchArticles' looks likes this:

class func fetchArticles(referringTile:Tile,completion:(articles:[Article])->(Void),
failure:(error:NSError)->(Void))

I've also tried declaring the function as 'public' but it didn't work.