How to use NSubstitute to mock a lazy class
//Assert
Lazy<INotificationService> notificationService = Substitute.For<Lazy<INotificationService>>();
Service target = new Service(repository, notificationService);

//Act
target.SendNotify("Message");

//Arrange
notificationService.Received().Value.sendNotification(null, null, null, null);

var notificationService = Substitute.For<INotificationService>();
var target = new Service(repository, new Lazy<INotificationService>(() => notificationService));

target.SendNotify("Message");

notificationService.ReceivedWithAnyArgs().sendNotification(null, null, null, null);