Implemented some test cases for the Fetcher class and the URL+Device extension.

README.md

@@ -11,4 +11,4 @@ Currently, this package contains the following libraries:
 * `Coordination`: protocols to implement the [Coordinator pattern](https://khanlou.com/2015/01/the-coordinator/) and some ready-to-use platform-specific concrete routers; 
 * `Core`: extensions we usually add to the base layer functionality and primitive types provided by the [Swift standard library](https://https://www.swift.org/documentation/#standard-library);
 * `Dependencies`: a ready-to-use, simple [Dependency Injection](https://en.wikipedia.org/wiki/Dependency_injection) mechanism that levers heavily on the [dynamic property wrappers](https://www.hackingwithswift.com/plus/intermediate-swiftui/creating-a-custom-property-wrapper-using-dynamicproperty) provided by the [Swift programming language](https://docs.swift.org/swift-book/documentation/the-swift-programming-language/properties/#Projecting-a-Value-From-a-Property-Wrapper);
-* `Persistence`: protocols, extensions and a ready-to-use fetcher class to simplify the building of the **CoreData** persistence layer;
+* `Persistence`: protocols, extensions and a ready-to-use fetcher class to simplify the building of the [CoreData](https://developer.apple.com/documentation/coredata) persistence layer;

Sources/Persistence/Classes/Fetcher.swift

@@ -62,21 +62,25 @@ public class Fetcher<Model: NSManagedObject>: NSObject, NSFetchedResultsControll
     /// Retrieve the number of objects in a given section number.
     /// - Parameter section: The section number to inquiry about.
     /// - Returns: A number of objects in the given section number.
-    public func numberOfObjectsInSection(_ section: Int) -> Int {
-        guard
-            let sections = fetchedResultsController.sections,
-            sections.endIndex > section
-        else {
-            return 0
+    public func numberOfObjects(in section: Int) throws -> Int {
+        guard let sections = fetchedResultsController.sections else {
+            throw FetcherError.fetchNotExecuted
         }
-        
+        guard sections.endIndex > section else {
+            throw FetcherError.sectionNotFound
+        }
+
         return sections[section].numberOfObjects
     }
     
     /// Retrieve an object out of a given index path.
     /// - Parameter indexPath: The index path to use to retrieve an object.
     /// - Returns: A `NSManagedObject` entity positioned in the given index path.
-    public func object(at indexPath: IndexPath) -> Model {
+    public func object(at indexPath: IndexPath) throws -> Model {
+        guard fetchedResultsController.sections != nil else {
+            throw FetcherError.fetchNotExecuted
+        }
+
         return fetchedResultsController.object(at: indexPath)
     }
 
@@ -134,6 +138,13 @@ public class Fetcher<Model: NSManagedObject>: NSObject, NSFetchedResultsControll
 
 }
 
+// MARK: - Errors
+
+public enum FetcherError: Error {
+    case fetchNotExecuted
+    case sectionNotFound
+}
+
 // MARK: - Enumerations
 
 public enum Change: Hashable {

Sources/Persistence/Protocols/Service.swift

@@ -27,10 +27,10 @@ public protocol Service {
     
     /// Save a given context.
     /// - Parameter context: A `NSManagedObjectContext` context instance to save.
-    func save(context: NSManagedObjectContext)
+    func save(context: NSManagedObjectContext) throws
     
     /// Save a given child context as well as its respective parent context.
     /// - Parameter context: A child `NSManagedObjectContext` context instance to save.
-    func save(childContext context: NSManagedObjectContext)
+    func save(childContext context: NSManagedObjectContext) throws 
     
 }

Tests/Persistence/Classes/FetcherTests.swift

@@ -0,0 +1,194 @@
+//
+//  FetcherTests.swift
+//  PersistenceTests
+//
+//  Created by Javier Cicchelli on 17/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import Persistence
+import XCTest
+
+final class FetcherTests: XCTestCase {
+
+    // MARK: Properties
+    
+    private let persistence = TestPersistenceService.shared
+    
+    private var fetcher: Fetcher<TestEntity>!
+    
+    // MARK: Setup
+    
+    override func setUpWithError() throws {
+        fetcher = .init(
+            fetchRequest: .allTestEntities(),
+            managedObjectContext: persistence.viewContext
+        )
+    }
+    
+    override func tearDownWithError() throws {
+        fetcher = nil
+    }
+    
+    // MARK: Number of sections tests
+    
+    func test_numberOfSections_whenModelIsEmpty() throws {
+        // GIVEN
+        try fetcher.fetch()
+        
+        // WHEN
+        let numberOfSections = fetcher.numberOfSections
+        
+        // THEN
+        XCTAssertEqual(numberOfSections, 1)
+    }
+    
+    func test_numberOfSections_whenModelIsFilled() throws {
+        // GIVEN
+        let context = persistence.makeChildContext()
+        let _ = [
+            TestEntity(context: context),
+            TestEntity(context: context),
+            TestEntity(context: context)
+        ]
+        
+        try persistence.save(childContext: context)
+        try fetcher.fetch()
+        
+        // WHEN
+        let numberOfSections = fetcher.numberOfSections
+        
+        // THEN
+        XCTAssertEqual(numberOfSections, 1)
+    }
+    
+    func test_numberOfSections_whenNoFetch() async throws {
+        // GIVEN
+        // WHEN
+        let numberOfSections = fetcher.numberOfSections
+        
+        // THEN
+        XCTAssertEqual(numberOfSections, 0)
+    }
+    
+    // MARK: Number of objects tests
+    
+    func test_numberOfObjects_inFirstSection_whenModelIsEmpty() throws {
+        // GIVEN
+        try fetcher.fetch()
+
+        // WHEN
+        let section = fetcher.numberOfSections - 1
+        let numberOfObjects = try fetcher.numberOfObjects(in: section)
+        
+        // THEN
+        XCTAssertEqual(numberOfObjects, 0)
+    }
+    
+    func test_numberOfObjects_inFirstSection_whenModelIsFilled() throws {
+        // GIVEN
+        let context = persistence.makeChildContext()
+        let entities = [
+            TestEntity(context: context),
+            TestEntity(context: context),
+            TestEntity(context: context)
+        ]
+        
+        try persistence.save(childContext: context)
+        try fetcher.fetch()
+
+        // WHEN
+        let section = fetcher.numberOfSections - 1
+        let numberOfObjects = try fetcher.numberOfObjects(in: section)
+        
+        // THEN
+        XCTAssertEqual(numberOfObjects, entities.count)
+    }
+    
+    func test_numberOfObjects_inNonExistingSection() throws {
+        // GIVEN
+        try fetcher.fetch()
+
+        // WHEN & THEN
+        let section = fetcher.numberOfSections
+        
+        XCTAssertThrowsError(try fetcher.numberOfObjects(in: section)) { error in
+            XCTAssertEqual(error as? FetcherError, .sectionNotFound)
+        }
+    }
+    
+    func test_numberOfObjects_whenNoFetch() throws {
+        // GIVEN
+        // WHEN & THEN
+        XCTAssertThrowsError(try fetcher.numberOfObjects(in: 1)) { error in
+            XCTAssertEqual(error as? FetcherError, .fetchNotExecuted)
+        }
+    }
+    
+    // MARK: Object at tests
+    
+    func test_objectAt_whenModelIsEmpty() throws {
+        // GIVEN
+        try fetcher.fetch()
+
+        // WHEN & THEN
+        let indexPath = IndexPath(
+            item: 0,
+            section: fetcher.numberOfSections - 1
+        )
+        
+        // TODO: Need to find out how to handle NSInvalidArgumentException in this test.
+        // let object = try fetcher.object(at: indexPath)
+    }
+    
+    func test_objectAt_whenModelIsFilled() throws {
+        // GIVEN
+        let context = persistence.makeChildContext()
+        let entities = [TestEntity(context: context)]
+        
+        try persistence.save(childContext: context)
+        try fetcher.fetch()
+
+        // WHEN & THEN
+        let indexPath = IndexPath(
+            item: entities.count - 1,
+            section: fetcher.numberOfSections - 1
+        )
+        
+        let object = try fetcher.object(at: indexPath)
+        
+        XCTAssertNotNil(object)
+    }
+    
+    func test_objectAt_withOutOfBoundsIndexPath() throws {
+        // GIVEN
+        let context = persistence.makeChildContext()
+        let entities = [TestEntity(context: context)]
+        
+        try persistence.save(childContext: context)
+        try fetcher.fetch()
+
+        // WHEN & THEN
+        let indexPath = IndexPath(
+            item: entities.count,
+            section: fetcher.numberOfSections
+        )
+
+        // TODO: Need to find out how to handle NSInvalidArgumentException in this test.
+        // let object = try fetcher.object(at: indexPath)
+    }
+
+    func test_objectAt_whenNoFetch() throws {
+        // GIVEN
+        // WHEN & THEN
+        let indexPath = IndexPath(
+            item: 0,
+            section: 0
+        )
+        
+        XCTAssertThrowsError(try fetcher.object(at: indexPath)) { error in
+            XCTAssertEqual(error as? FetcherError, .fetchNotExecuted)
+        }
+    }
+    
+}

Tests/Persistence/Extensions/URL+DevicesTests.swift

@@ -0,0 +1,30 @@
+//
+//  URL+DevicesTests.swift
+//  PersistenceTests
+//
+//  Created by Javier Cicchelli on 17/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import Foundation
+import Persistence
+import XCTest
+
+final class URL_DevicesTests: XCTestCase {
+    
+    // MARK: Properties
+    
+    private var url: URL!
+    
+    // MARK: - Tests
+    
+    func test_bitBucket() {
+        // GIVEN
+        // WHEN
+        url = .bitBucket
+        
+        // THEN
+        XCTAssertEqual(url.absoluteString, "file:///dev/null")
+    }
+    
+}

Tests/Persistence/Helpers/NSFetchRequest+TestEntity.swift

@@ -0,0 +1,24 @@
+//
+//  NSFetchRequest+TestEntity.swift
+//  PersistenceTests
+//
+//  Created by Javier Cicchelli on 17/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import CoreData
+
+extension NSFetchRequest where ResultType == TestEntity {
+    
+    // MARK: Functions
+    
+    static func allTestEntities() -> NSFetchRequest<TestEntity> {
+        let request = TestEntity.fetchRequest()
+        
+        request.sortDescriptors = []
+        request.resultType = .managedObjectResultType
+        
+        return request
+    }
+
+}

Tests/Persistence/Helpers/TestModel.xcdatamodeld/Model.xcdatamodel/contents

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<model type="com.apple.IDECoreDataModeler.DataModel" documentVersion="1.0" lastSavedToolsVersion="21754" systemVersion="22E261" minimumToolsVersion="Automatic" sourceLanguage="Swift" userDefinedModelVersionIdentifier="">
+    <entity name="TestEntity" representedClassName="TestEntity" syncable="YES" codeGenerationType="class"/>
+</model>

Tests/Persistence/Helpers/TestPersistenceService.swift

@@ -0,0 +1,127 @@
+//
+//  TestPersistenceService.swift
+//  PersistenceTests
+//
+//  Created by Javier Cicchelli on 17/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import CoreData
+import Persistence
+
+struct TestPersistenceService {
+    
+    // MARK: Properties
+    
+    static let shared = TestPersistenceService()
+    
+    private let container: NSPersistentContainer
+    
+    var viewContext: NSManagedObjectContext {
+        container.viewContext
+    }
+    
+    // MARK: Initialisers
+    
+    init() {
+        guard
+            let modelURL = Bundle.module.url(forResource: .Model.name, withExtension: .Model.extension),
+            let managedObjectModel = NSManagedObjectModel(contentsOf: modelURL)
+        else {
+            fatalError("Could not load the Core Data model from the module.")
+        }
+        
+        self.container = .init(
+            name: .Model.name,
+            managedObjectModel: managedObjectModel
+        )
+        
+        setContainer()
+    }
+
+}
+
+// MARK: - Service
+
+extension TestPersistenceService: Service {
+    
+    // MARK: Functions
+    
+    func makeTaskContext() -> NSManagedObjectContext {
+        let taskContext = container.newBackgroundContext()
+        
+        taskContext.automaticallyMergesChangesFromParent = true
+        taskContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
+        
+        return taskContext
+    }
+    
+    func makeChildContext() -> NSManagedObjectContext {
+        let context = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
+        
+        context.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
+        context.parent = container.viewContext
+        context.automaticallyMergesChangesFromParent = true
+        
+        return context
+    }
+    
+    func save(context: NSManagedObjectContext) throws {
+        guard context.hasChanges else {
+            return
+        }
+        
+        try context.save()
+    }
+    
+    func save(childContext context: NSManagedObjectContext) throws {
+        guard context.hasChanges else {
+            return
+        }
+        
+        try context.save()
+        
+        guard
+            let parent = context.parent,
+            parent == container.viewContext
+        else {
+            return
+        }
+
+        try parent.performAndWait {
+            try parent.save()
+        }
+    }
+    
+}
+
+// MARK: - Helpers
+
+private extension TestPersistenceService {
+    
+    // MARK: Functions
+    
+    func setContainer() {
+        container.persistentStoreDescriptions = [
+            .init(url: .bitBucket)
+        ]
+        
+        container.loadPersistentStores { _, error in
+            if let error = error as NSError? {
+                fatalError("Unresolved error \(error), \(error.userInfo)")
+            }
+        }
+        
+        container.viewContext.automaticallyMergesChangesFromParent = false
+    }
+
+}
+
+// MARK: - String+Constants
+
+private extension String {
+    enum Model {
+        static let name = "TestModel"
+        static let `extension` = "momd"
+    }
+}