public void NotificationRepository_DeleteByUserId_DeletesNotifications() { //arrange INotificationRepo nr = GetInMemoryNotificationRepository(); Notification notification2 = new Notification { Type = "like", ReceiverId = 1, SenderId = 3, Status = true, ReviewId = 2 }; //act nr.Add(notification); nr.Add(notification2); nr.DeleteByUserId(1); //both notifications have same receiver id //assert Assert.ThrowsAny <ArgumentNullException>(() => nr.GetById(1)); Assert.ThrowsAny <ArgumentNullException>(() => nr.GetById(2)); }