here's the code from my test

this is my test

        [Test]
        public void TestValidateEmail()
        {

            CustomerAddress customerAddressController = new CustomerAddress();

            string messageGood = customerAddressController.Rules.ValidateEmail("name@domain.com");
            Assert.IsNullOrEmpty(messageGood);

            string messageBad = customerAddressController.Rules.ValidateEmail("name@domain,com");
            Assert.IsNotNullOrEmpty(messageBad);
        }

this is the rule

       public string ValidateEmail(string email)
        {
            string msg = null;
            if (!Validate.Email(email))
            {
                this.EntityPropertyDisplayName = "Customer Email";

                msg = this.EntityPropertyDisplayName + " is not a valid email address!";

                AddErrorProviderWarning("Email", msg);
            }
            return msg;
        }

this is the Validate.Email method

	public static bool Email(string email)
        {
            string patternStrict = @"^(([^<>()[\]\\.,;:\s@\""]+"
                  + @"(\.[^<>()[\]\\.,;:\s@\""]+)*)|(\"".+\""))@"
                  + @"((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}"
                  + @"\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+"
                  + @"[a-zA-Z]{2,}))$";

            Regex matcher = new Regex(patternStrict);
            bool isMatch = matcher.IsMatch(email);
            return isMatch;
        }