iOS - Mocking UserDefault before loading the view controller - ios

Question

I am currently working on test for my application and I have faced a problem when mocking user defaults. Let me first show you my setup :
this is how I mock user Defaults :
class MockUserDefaults: UserDefaults {
typealias FakeData = Dictionary<String, Any?>
var data: FakeData
convenience init() {
self.init(suiteName: "mocking")!
}
override init?(suiteName suitename: String?) {
data = FakeDefaults()
UserDefaults().removePersistentDomain(forName: suitename!)
super.init(suiteName: suitename)
}
override func object(forKey defaultName: String) -> Any? {
if let data = data[defaultName] {
return data
}
return nil
}
override func set(_ value: Any?, forKey defaultName: String) {
if defaultName == "favs"{
data[defaultName] = value
}
}
}
I have a variable in my view controller called : userDefaults, and I set it like this :
var userDefaults : UserDefaults {
if (NSClassFromString("XCTest") != nil) {
return MockUserDefaults()
}
return UserDefaults.standard
}
this variable is actually an extension to a protocol which a made uiviewcontroller conform to it to make sure all my view controllers have this variable.
I also have a variable in myViewcontroller called favoriteMovie which I set like this :
private var favoriteMovie: Favorite? {
if let favoriteString = userDefaults.value(forKey: "favs") as? String {
return favorites.first(where: {$0.name == favoriteString})
}
return nil
}
now here's where the problem is, when I go and try to test this view controller , I need to set userDefault with an object for example :
myviewController.userDefaults.set("avengers", forKey: "favs")
before the test runs, but the problem is that favoriteMovie variable always return nil and I need it to return an object before the test runs . Any help. Thanks in advance.
UPDATE :
this is the protocol :
protocol Mockable: class {
var userDefaults: UserDefaults { get }
}
this is the extension :
extension UIViewController: Mockable {}
extension Mockable {
var userDefaults : UserDefaults {
if (NSClassFromString("XCTest") != nil) {
return MockUserDefaults()
}
return UserDefaults.standard
}
}

Answer 1

Here are two ways to fix it.
1) By doing some DI. In you viewController declare userDefaults as non-computed property as below
var userDefaults : UserDefaults?
In your test case, create MockUserDefaults object, set values and assign it to viewController when you are initiating it as below,
let mockUD = MockUserDefaults()
mockUD.set("avengers", forKey: "favs")
myviewController.userDefaults = mockUD
Now you will get the avengers object.
2) As the question is updated, here is the fix to hold the mockDefaults object,
struct AssociatedMock {
static var key: UInt8 = 0
}
extension Mockable {
private (set) var _mockDefaults: MockUserDefaults? {
get {
guard let value = objc_getAssociatedObject(self, &AssociatedMock.key) as? MockUserDefaults else {
return nil
}
return value
}
set(newValue) {
objc_setAssociatedObject(self, &AssociatedMock.key, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
}
var userDefaults : UserDefaults {
if (NSClassFromString("XCTest") != nil) {
if self._mockDefaults == nil {
self._mockDefaults = MockUserDefaults()
}
return self._mockDefaults!
}
return UserDefaults.standard
}
}