Dependencies.swift

protocol RemoteAPIDelegate: class {
    func remoteAPIDidLoadPosts(_ posts: NSArray)
}

class RemoteAPI {

    weak var delegate: RemoteAPIDelegate?

    func loadPosts() {

    }
}

class FeedViewModel: RemoteAPIDelegate {

    private let remoteAPI: RemoteAPI
    private var initialPostsLoaded = false

    init(remoteAPI: RemoteAPI) {
        self.remoteAPI = remoteAPI
    }

    func loadInitialPosts() {
        // how to test this method?
        if (initialPostsLoaded) {
            return
        }

        remoteAPI.loadPosts()
    }

    func remoteAPIDidLoadPosts(_ posts: NSArray) {
        initialPostsLoaded = true
    }
}

// factory code

let remoteAPI = RemoteAPI()
let viewModel = FeedViewModel(remoteAPI: remoteAPI)
remoteAPI.delegate = viewModel