How to validate an object

SingerTests.cs

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace QuickTests
{
    [TestClass]
    public class SingerTests
    {
        public class Singer
        {
            [Required, StringLength(20)]
            public string FirstName { get; set; }

            [Required, StringLength(20)]
            public string LastName { get; set; }
        }

        [TestMethod]
        public void RequiredFieldsValidatedFirst()
        {
            var cher = new Singer { FirstName = "The artist formerly known as" };
            var vc = new ValidationContext(cher, null, null);
            var results = new List<ValidationResult>();

            // Ensure required fields are met and object-level validation is valid
            var isValid = Validator.TryValidateObject(cher, vc, results);

            Assert.IsFalse(isValid);
            Assert.AreEqual(1, results.Count);
        }

        [TestMethod]
        public void PropertyValuesNotValidatedByDefault()
        {
            var cher = new Singer { FirstName = "The artist formerly known as", LastName = "Prince" };
            var vc = new ValidationContext(cher, null, null);
            var results = new List<ValidationResult>();

            // By default, property values are not validated, as they were most-likely validated
            // while being set.
            var isValid = Validator.TryValidateObject(cher, vc, results);

            Assert.IsTrue(isValid);
            Assert.AreEqual(0, results.Count);
        }

        [TestMethod]
        public void PropertyValuesCanBeValidatedToo()
        {
            var cher = new Singer { FirstName = "The artist formerly known as", LastName = "Prince" };
            var vc = new ValidationContext(cher, null, null);
            var results = new List<ValidationResult>();

            // By default, property values are not validated, as they were most-likely validated
            // while being set.  But you can force property value validation too.
            var isValid = Validator.TryValidateObject(cher, vc, results, validateAllProperties: true);

            Assert.IsFalse(isValid);
            Assert.AreEqual(1, results.Count);
        }
    }
}