Swift MVVM testing strategy and code coverage questions - swift

Question

I've run into an issue when generating code coverage with Xcode for view models in an MVVM environment.
Our basic setup is the view controller makes requests to the view model, which in turn calls methods on a data manager that talks to web services.
I came up with what I thought was a reasonably elegant way to test the view models by creating a fake data manager that subclasses the actual data manager and overrides the function called by the VM.
The problem is that for this to work, the VM must be part of the app target and the test target. An apparent side effect of this is that code coverage is not generated for items belonging to two or more targets, even though the unit tests pass. Code coverage is enabled in the project.
Here is a excerpted view model:
import Foundation
class BoosViewModel: BaseViewModel {
convenience override init() {
self.init(dataManager: BoosDataManager(), andModel: nil)
}
func getUnlinkedBoos(_ cardType: CardType) {
(dataManager as! BoosDataManager).getUnlinkedBoos(cardType) { result, error in
...stuff happens here...
}
}
}
... and the data manager
class BoosDataManager: DataManager {
static let SharedInstance: BoosDataManager = {
var manager = BoosDataManager()
return manager
}()
func getUnlinkedBoos(_ cardType: CardType = .loyalty, completion: #escaping ((_ result: BoosModel?, _ error: NSError?) -> Void)) {
...stuff happens here...
}
}
...and the test
class BoosViewModelTests: XCTestCase {
func testGetUnlinkedBoosHappyPath() {
class FauxDataManager: BoosDataManager {
override func getUnlinkedBoos(_ cardType: CardType = .loyalty, completion: #escaping ((_ result: BoosModel?, _ error: NSError?) -> Void)) {
...stuff happens here...
}
}
let viewModel = BoosViewModel()
let dataManager = FauxDataManager()
viewModel.dataManager = dataManager
viewModel.getUnlinkedBoos(.loyalty)
XCTAssertTrue(testObserver.updated)
XCTAssertEqual(testObserver.newViewModel.getBoos().count, 1)
}
}
As I noted earlier the unit tests in this scenario complete successfully, but unit coverage does not get generated.
I have older tests where I actually created an external fake data manager class that was used by the test, the class under test is not part of the test target, and coverage works fine.
The drawback to that is that I have to create multiple data managers to handle specific cases for its returns. If I can't encapsulate the classes, I would need to create a bunch of swift data managers, one for each scenario.
That's why I came up with the internal class.
Now, the problem comes in if I remove the view model under test from the testing target. After doing this, I add #testable import BoosApp to the unit test so that the view model under test can be resolved. When I do this, I get the following error:
Could not cast value of type 'BoosTests.BoosViewModelTests.(testGetUnlinkedBoosHappyPath () -> ()).(FauxDataManager #1)' (0x11f673d18) to 'Boos.BoosDataManager' (0x10444b128).
Aug 30 20:43:01 Pay[19025] : Could not cast value of type 'BoosTests.BoosViewModelTests.(testGetUnlinkedBoosHappyPath () -> ()).(FauxDataManager #1)' (0x11f673d18) to 'Boos.BoosDataManager' (0x10444b128).
I'm not sure what I'm missing. Is there a way to make this scenario work, or am I stuck creating multiple data managers outside of the test code?

Answer 1

Ultimately, I figured out the main issue was that the view model and data manager had somehow gotten added to the test target. After removing them from the test target I was able to make a couple of minor changes and everything is running fine. FYI.