public async void StudentId_Create_Valid_Reference()
        {
            Mock <IEventStudentRepository> eventStudentRepository = new Mock <IEventStudentRepository>();

            eventStudentRepository.Setup(x => x.StudentByStudentId(It.IsAny <int>())).Returns(Task.FromResult <Student>(new Student()));

            var validator = new ApiEventStudentServerRequestModelValidator(eventStudentRepository.Object);
            await validator.ValidateCreateAsync(new ApiEventStudentServerRequestModel());

            validator.ShouldNotHaveValidationErrorFor(x => x.StudentId, 1);
        }
        public async void EventId_Update_Invalid_Reference()
        {
            Mock <IEventStudentRepository> eventStudentRepository = new Mock <IEventStudentRepository>();

            eventStudentRepository.Setup(x => x.EventByEventId(It.IsAny <int>())).Returns(Task.FromResult <Event>(null));

            var validator = new ApiEventStudentServerRequestModelValidator(eventStudentRepository.Object);

            await validator.ValidateUpdateAsync(default(int), new ApiEventStudentServerRequestModel());

            validator.ShouldHaveValidationErrorFor(x => x.EventId, 1);
        }