How to create a mock view controller from storyboard-CodePudding

I'm trying to create a mock view controller for a view controller that was created from a storyboard.

If I try to downcast it as following, it doesn't work since the storyboard view controller is encoded:

let _storyboard = UIStoryboard(name: "Main", bundle: nil)
let vc = _storyboard.instantiateViewController(ofType: ViewController.self) as? MockViewController

where MockViewController is the subclass of ViewController.

I tried initializing the mock view controller using the nib name, but the nil error happens for the uninitialized @IBOutlet properties:

class MockViewController: ViewController {
    init() {
        let controllerName = String(describing: ViewController.self)
        super.init(nibName: controllerName, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

I could potentially create an identical view controller and initialize them manually:

let _storyboard = UIStoryboard(name: "Main", bundle: nil)
let vc = _storyboard.instantiateViewController(ofType: ViewController.self)
let mockViewController = MockViewController()
mockViewController.someProperty = vc.property

but doesn't seem very efficient and also it entails always manually coordinating changes in both the production code and the test code.

The most promising method I found was using this initializer:

let controllerName = String(describing: ViewController.self)
let mockVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(identifier: controllerName, creator: { coder -> MockViewController? in
    return MockViewController(coder: coder)
})

where the MockViewController is the subclass of ViewController again and has the following initializer:

required init?(coder: NSCoder) {
    super.init(coder: coder)
}

However, this also results in the same error as the first one where the @IBOutlet properties return nil errors.

CodePudding user response：

You're trying to use "Subclass and Override" to do partial mocking, so that you can record calls to the view controller. But this isn't possible on a view controller defined in a storyboard. As I write in my book,

Storyboard-based view controller can't be subclassed because the storyboard stores an instance of a predetermined type.

Alternatives:

Load your storyboard from a XIB instead of a Storyboard.
Define your UI programatticaly instead of in a Storyboard.
Have your Presenter use a protocol instead of a direct reference to your view controller. Then inject what you like.

CodePudding user response：

In the last scenario , is :

let controllerName = String(describing: ViewController.self)
let mockVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(identifier: controllerName, creator:
{ coder -> MockViewController? in
    return MockViewController(coder: coder)
})

Before try to access to outlets , you need to load the outlets of the page so below code could solve your problem. Just add it after mockVc definition

mockVC.loadView()