Hands-On Design Patterns with Swift

Enhanced testing

Because the whole state of the view can be tested externally, thanks to the MVVM pattern, we can write better and more maintainable code. Let's look at how we can properly test the logic of the ViewModel, in order to ensure that the views bound to it will react properly.

Ultimately, we need to ensure the following:

• When a question advances to the next one, the onQuestionChanged callback is properly called.
• When there are no more questions, getQuestionText() returns nil:

class ViewModelTesting: XCTestCase {    func testCallsNextQuestion() {        let questions = QuestionController(questions: [Question(question: "OK", answer: .true)])        let viewModel = ViewModel(questions: questions)        var called = false                viewModel.onQuestionChanged