Coder

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class StubContactsDataSource: ContactsDataSource {
    func getAll() -> [Contact] {
        return [Contact(name: "Stub 1"), Contact(name: "Stub 2")]
    }
}

// In your production code, you can use the default constructor. For example:

let productionContactsListViewController = ContactsListViewController()
productionContactsListViewController.showAllContacts() // Prints Andrea and Juan. It uses the default NetworkContactsDataSource.


// In your tests code, you can't use the default constructor, however, even though you can override the default dependency,
// if you want to use StubContactsDataSource you need to override all the dependencies using by default NetworkContactsDataSource.
// For example:

let presenter = ContactsListPresenter(getAllContacts: StubContactsDataSource())
let testContactsListViewController = ContactsListViewController(presenter: presenter)
testContactsListViewController.showAllContacts() // Prints Stub 1 and Stub 2

// As you can see, even though you want to override only the data source, you can't use the default presenter anymore.
// In this example I use a very simple dependency graph, but in a real app, this NetworkDataSource could be used by a lot of other clases
// You need to stop using the default constructor for all this clases to be able to replace the data source dependency. Again, all the
// clases depending in those clases can't use the default constructor recursively.


// With the proposed approach, overriding the data source for all the dependencies using it would be very easy:
class TestAssembler: ContactsSceneAssembler {
    func resolve() -> ContactsDataSource {
        return StubContactsDataSource()
    }
}