public async void FirstName_Update_null()
        {
            Mock <ICustomerRepository> customerRepository = new Mock <ICustomerRepository>();

            customerRepository.Setup(x => x.Get(It.IsAny <int>())).Returns(Task.FromResult(new Customer()));

            var validator = new ApiCustomerServerRequestModelValidator(customerRepository.Object);
            await validator.ValidateUpdateAsync(default(int), new ApiCustomerServerRequestModel());

            validator.ShouldHaveValidationErrorFor(x => x.FirstName, null as string);
        }
        public async void Email_Update_length()
        {
            Mock <ICustomerRepository> customerRepository = new Mock <ICustomerRepository>();

            customerRepository.Setup(x => x.Get(It.IsAny <int>())).Returns(Task.FromResult(new Customer()));

            var validator = new ApiCustomerServerRequestModelValidator(customerRepository.Object);
            await validator.ValidateUpdateAsync(default(int), new ApiCustomerServerRequestModel());

            validator.ShouldHaveValidationErrorFor(x => x.Email, new string('A', 129));
        }