public void ShouldNotAcceptInvalidChars(string creditCardNumber)
        {
            var validator = new CreditCardNumberValidator();

            var isValid = validator.Validate(creditCardNumber);

            isValid.Should().BeFalse();
        }
        public void ShouldNotAcceptInvalidLuhnCheck(string validCreditCard)
        {
            var validator = new CreditCardNumberValidator();

            var isValid = validator.Validate(validCreditCard);

            isValid.Should().BeFalse();
        }
        public void ShouldAcceptValidCreditCard(string creditCardNumber)
        {
            var validator = new CreditCardNumberValidator();

            var isValid = validator.Validate(creditCardNumber);

            isValid.Should().BeTrue();
        }