Initialize a managed object model with swift that will work for Tests and Application

managedObjectModel

lazy var managedObjectModel: NSManagedObjectModel = {
        // The managed object model for the application.
        let modelURL = NSBundle.mainBundle().URLForResource("<appName>", withExtension: "momd")!
        let managedObjectModel = NSManagedObjectModel(contentsOfURL: modelURL)!

        // Check is we are running as test or not
        let environment = NSProcessInfo.processInfo().environment as [String : AnyObject]
        let isTest = (environment["XCInjectBundle"] as? String)?.pathExtension == "xctest"

        // Create the module name
        let moduleName = (isTest) ? "<appName>Tests" : "<appName>"

        // Create a new managed object model with updated entity class names
        var newEntities = [] as [NSEntityDescription]
        for (_, entity) in enumerate(managedObjectModel.entities) {
            let newEntity = entity.copy() as NSEntityDescription
            newEntity.managedObjectClassName = "\(moduleName).\(entity.name)"
            newEntities.append(newEntity)
        }
        let newManagedObjectModel = NSManagedObjectModel()
        newManagedObjectModel.entities = newEntities

        return newManagedObjectModel
    }()