asp.net中的TDD新手,我是否在正确的轨道上编写测试？

using System;
using System.Text;
using System.Collections.Generic;
using System.Linq;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace MembershipTest.Tests
{
    [TestClass]
    public class CustomDataAnnotationsTest
    {
        [TestMethod]
        public void CustomDataAnnotations_Email_ReturnTrueIfNull()
        {
            // Arrange
            EmailAttribute attribute = new EmailAttribute();

            // Act
            bool result = attribute.IsValid(null);

            // Assert
            Assert.AreEqual(true,result);
        }

        [TestMethod]
        public void CustomDataAnnotations_Email_ReturnFalseIfInvalid()
        {
            // Arrange
            EmailAttribute attribute = new EmailAttribute();

            // Act
            bool result = attribute.IsValid("()[];:,<>@example.com");

            // Assert
            Assert.AreEqual(false,result);
        }

        [TestMethod]
        public void CustomDataAnnotations_Email_ReturnTrueIfValid()
        {
            // Arrange
            EmailAttribute attribute = new EmailAttribute();

            // Act
            bool result = attribute.IsValid("john.smith@example.com");

            // Assert
            Assert.AreEqual(true,result);
        }
    }
}

以下是为测试编写的后续代码：

using System;
using System.ComponentModel.DataAnnotations;
using System.Net.Mail;

public class EmailAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        //Let RequiredAttribute validate whether the value is required or not.
        if (value == null)
        {
            return true;
        }

        //Check to see if System.Net.Mail can send to the address.
        try
        {
            var i = new MailAddress(value.ToString());
        }
        catch (Exception)
        {
            return false;
        }

        return true;
    }

}

所有测试最初都失败了,然后在编写代码后成功,但测试是否写得恰当？太多或太少？我知道这是一个非常简单的例子,但我想确保自己走上正确的轨道,然后才能开始更复杂的事情.