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

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 
     
 }