I want to create a MVVM-C project, but also adequately test it. Naturally I want to create such a project that can access a Network Service.

Any comments or thoughts on this approach?

DependencyFactory:

protocol Factory {
    var networkManager: HTTPManagerProtocol { get }
    func makeInitialViewModel(coordinator: Coordinator) -> InitialViewModel
    func makeInitialView(viewModel: InitialViewModel) -> InitialView
    func makeDetailView(viewModel: DetailViewModel) -> DetailView
    func makeDetailViewModel(coordinator: Coordinator) -> DetailViewModel
}

// replace the DependencyContainer for tests
class DependencyFactory: Factory {
    var networkManager: HTTPManagerProtocol = HTTPManager()
    
    // should not return an optional at the end of this project
    func makeInitialCoordinator() -> ProjectCoordinator {
        let coordinator = ProjectCoordinator(factory: self)
        return coordinator
    }
    
    func makeInitialView(viewModel: InitialViewModel) -> InitialView {
        let view = InitialView()
        return view
    }
    
    func makeInitialViewModel(coordinator: Coordinator) -> InitialViewModel {
        let viewModel = InitialViewModel(coordinator: coordinator, networkManager: networkManager)
        return viewModel
    }
    
    func makeDetailView(viewModel: DetailViewModel) -> DetailView {
        let view = DetailView()
        return view
    }
    
    func makeDetailViewModel(coordinator: Coordinator) -> DetailViewModel {
        let viewModel = DetailViewModel(coordinator: coordinator, networkManager: networkManager)
        return viewModel
    }
}

A basic HTTPManager (that doesn't really touch the network, but you get the point!)

protocol HTTPManagerProtocol {
    func get(url: URL, completionBlock: @escaping (Result<Data, Error>) -> Void)
}

class HTTPManager: HTTPManagerProtocol {
    public func get(url: URL, completionBlock: @escaping (Result<Data, Error>) -> Void) {
        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
            let data = Data("The Data from HTTPManager".utf8)
            completionBlock(.success(data))
        }
    }
}

Project Coordinator

protocol Coordinator: class {
    func start(_ navigationController: UINavigationController)
    func moveToDetail()
}

class ProjectCoordinator: Coordinator {
    var childCoordinators = [Coordinator]()
    var navigationController: UINavigationController?
    
    private var factory: Factory

    init(factory: Factory) {
        self.factory = factory
    }

    func start(_ navigationController: UINavigationController) {
        let vc = InitialViewController(factory: factory, coordinator: self)
        self.navigationController = navigationController
        navigationController.pushViewController(vc, animated: true)
    }
    
    func moveToDetail() {
        let vc = DetailViewController(factory: factory, coordinator: self)
        navigationController?.pushViewController(vc, animated: true)
    }
}

InitialModel

struct InitialModel : Codable {
    let dataString : String
}

InitialView

final class InitialView: UIView {

    let traverseButton = UIButton(type: .custom)
    let networkButton = UIButton(type: .custom)
    let networkLabel = UILabel()
    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    private func setup() {
        self.backgroundColor = .red
        traverseButton.frame = CGRect(x: 0, y: 0, width: 200, height: 100)
        traverseButton.setTitle("Go to Detail", for: .normal)
        traverseButton.setTitleColor(.black, for: .normal)
        traverseButton.isUserInteractionEnabled = true
                
        self.addSubview(traverseButton)
        traverseButton.translatesAutoresizingMaskIntoConstraints = false
        traverseButton.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
        traverseButton.centerYAnchor.constraint(equalTo: self.centerYAnchor).isActive = true
        
        networkButton.frame = CGRect(x: 0, y: 0, width: 200, height: 100)
        networkButton.setTitle("Make Network Call", for: .normal)
        networkButton.setTitleColor(.black, for: .normal)
        networkButton.isUserInteractionEnabled = true
        
        self.addSubview(networkButton)
        networkButton.translatesAutoresizingMaskIntoConstraints = false
        networkButton.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
        networkButton.centerYAnchor.constraint(equalTo: self.centerYAnchor, constant: 100).isActive = true
        
        networkLabel.text = "No network calls made"
        networkLabel.backgroundColor = .purple
        self.addSubview(networkLabel)
        
        networkLabel.translatesAutoresizingMaskIntoConstraints = false
        networkLabel.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
        networkLabel.centerYAnchor.constraint(equalTo: self.centerYAnchor, constant: 200).isActive = true
        networkLabel.widthAnchor.constraint(equalToConstant: 300).isActive = true
        networkLabel.heightAnchor.constraint(equalToConstant: 100).isActive = true
    }
    
    func setNetworkLabel(text: String){
        networkLabel.text = text
    }

}

InitialViewController

class InitialViewController: UIViewController {
    private var coordinator: Coordinator?
    private var factory: Factory?
    
    var intialView: InitialView?
    
    lazy var viewModel: InitialViewModel? = {
        return factory?.makeInitialViewModel(coordinator: coordinator!)
    }()
    
    init(factory: Factory, coordinator: Coordinator) {
        self.factory = factory
        self.coordinator = coordinator
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func loadView() {
        if let initialView = factory?.makeInitialView(viewModel: viewModel!) {
            initialView.traverseButton.addTarget(self, action: #selector(traverseButton(_:)), for: .touchDown)
            initialView.networkButton.addTarget(self, action: #selector(networkButton), for: .touchDown)
            self.intialView = initialView
            self.view = initialView
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    @IBAction func traverseButton(_ sender: UIButton) {
        coordinator?.moveToDetail()
    }
    
    @IBAction func networkButton(_ sender: UIButton) {
        viewModel?.fetchData(completion: { data in
            switch data {
            case .failure: fatalError()
            case .success(let data):
                if let data = data.first {
                    self.intialView?.setNetworkLabel(text: data.dataString)
                }
            }
        })
    }

}

InitialViewModel

class InitialViewModel {
    private var networkManager: HTTPManagerProtocol?
    init(coordinator: Coordinator?, networkManager: HTTPManagerProtocol) {
        self.networkManager = networkManager
    }
    
    func fetchData(completion: @escaping (Result<[InitialModel], Error>) -> Void) {
        networkManager?.get(url: URL(string: "NOURL")!, completionBlock: { result in
            DispatchQueue.main.async {
                switch result {
                case .failure:
                    completion(.failure(NSError()))
                case .success(let data):
                    if let str = String(data: data, encoding: .utf8) {
                        let model = InitialModel(dataString: str)
                        completion(.success([model]))
                    }
                }
            }
        })
    }
}

DetailViewController

class DetailViewController: UIViewController {
    weak var coordinator: Coordinator?
    private var factory: Factory?

    var detailView: DetailView?
    
    lazy var viewModel: DetailViewModel? = {
        return factory?.makeDetailViewModel(coordinator: coordinator!)
    }()
    
    init(factory: Factory, coordinator: Coordinator) {
        self.factory = factory
        self.coordinator = coordinator
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func loadView() {
        if let detailView = factory?.makeDetailView(viewModel: viewModel!) {
            self.detailView = detailView
            self.view = detailView
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
    }
}

DetailViewModel

class DetailViewModel {
    private var networkManager: HTTPManagerProtocol?
    init(coordinator: Coordinator?, networkManager: HTTPManagerProtocol) {
        self.networkManager = networkManager
    }
}

DetailView

final class DetailView: UIView {
    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    private func setup() {
        self.backgroundColor = .blue
    }
}