Using a mocked Core Data container with background processes - ios

Question

I implemented unit testing with my Swift iOS app that uses Core Data, but I am having trouble getting unit tests to pass. I referenced the guide linked below and some stack overflow threads, but I'm still having trouble.
The app runs without flaws when actually built, but the tests fail, leading me to believe that I've messed up somewhere with integrating the mocked the Core Data container and background persistent containers. However, I can't seem to figure out where I'm going wrong here, so any advice is appreciated.
I apologize if my post is lacking any key details, but I'll add them in as necessary.
Main reference material: Cracking the Tests for Core Data
Test Code
class MealTests: XCTestCase {
var sut: MealController!
lazy var managedObjectModel: NSManagedObjectModel = {
let managedObjectModel = NSManagedObjectModel.mergedModel(from: [Bundle(for: type(of: self))])!
return managedObjectModel
}()
lazy var mockPersistentContainer: NSPersistentContainer = {
let container = NSPersistentContainer(name: "WeeklyModel", managedObjectModel: self.managedObjectModel)
let description = NSPersistentStoreDescription()
description.type = NSInMemoryStoreType
description.shouldAddStoreAsynchronously = false
container.persistentStoreDescriptions = [description]
container.loadPersistentStores {(description, error) in
//Double check to confirm that date store is in memory
precondition(description.type == NSInMemoryStoreType)
//Check for errors
if let error = error {
fatalError("Creating an in-memory coordinator failed")
}
}
return container
}()
override func setUp() {
super.setUp()
sut = MealController(tense: .all, persistentContainer: mockPersistentContainer)
}
func test_CreatingNewMeal_IsNotNilAndPropertiesSetCorrectly() {
let mealType = Int16(1)
let date = NSDate(timeIntervalSinceNow: 0.0)
let mealDescription = "Testy McTestFace"
let servings = Int16(1)
let image = UIImage(named: "Recipe")
let favorite = false
let meal = sut.saveLocalMeal(mealType: mealType, date: date, mealDescription: mealDescription, servings: servings, image: image, favorite: favorite)
//Test meal is not nil
XCTAssertNotNil(meal, "Should not be nil")
//Testing creating meal sets all properties correctly
XCTAssertEqual(meal?.meal, mealType)
}
Controller Class
class MealController {
//MARK: - Properties
//<...>
private let persistentContainer: NSPersistentContainer!
private var fetchedResultsController: NSFetchedResultsController<Meal>!
lazy var backgroundMOC: NSManagedObjectContext = {
return self.persistentContainer.newBackgroundContext()
}()
//Set to standard persistence container by default
init(tense: Tense, persistentContainer: NSPersistentContainer) {
self.persistentContainer = persistentContainer
self.persistentContainer.viewContext.automaticallyMergesChangesFromParent = true
reloadAllLocalData(for: tense)
}
convenience init(tense: Tense) {
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
fatalError("Could not set Managed Object Context")
}
self.init(tense: tense, persistentContainer: appDelegate.persistenceContainer)
}
func getMealCount() -> Int {
return fetchedResultsController.fetchedObjects?.count ?? 0
}
func getMeal(at indexPath: IndexPath) -> Meal {
return fetchedResultsController.object(at: indexPath)
}
//The boolean determines whether historical or future data is shown
func reloadAllLocalData(for tense: Tense){
let fetchRequest: NSFetchRequest<Meal> = Meal.fetchRequest()
//Setting predicate, etc.
//<...>
fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: backgroundMOC, sectionNameKeyPath: nil, cacheName: nil)//Add cache to this?
do {
try fetchedResultsController.performFetch()
} catch let error {
//<...>
}
}
//Saving
func saveLocalMeal(mealType: Int16, date: NSDate, mealDescription: String, servings: Int16, image: UIImage?, favorite: Bool, comment: String? = nil, recipeUID: String? = nil) -> Meal? {
//Make new meal object
let meal = Meal(entity: Meal.entity(), insertInto: backgroundMOC)
//Call helper func and result result
return save(context: backgroundMOC, meal: meal, mealUID: nil, mealType: mealType, date: date, mealDescription: mealDescription, servings: servings, image: image, favorite: favorite, comment: comment, recipeUID: recipeUID)
}
private func save(context: NSManagedObjectContext, meal: Meal, mealUID: String?, mealType: Int16, date: NSDate, mealDescription: String, servings: Int16, image: UIImage?, favorite: Bool, comment: String? = nil, recipeUID: String? = nil) -> Meal? {
//Setting properties
//<...>
do {
try backgroundMOC.save()
return meal
} catch let error as NSError {
print("Could not save. \(error)")
return nil
}
}