Example of a shallow copy of a CLR generic List<T>

shallowCopy.cs

namespace Test
{

    public static class ExtMethods
    {

        public static List<T> Clone<T>(this List<T> thisList)
        {
            // For-loop allows for later management of the copy..  if we wanted to perform additional operations later
            
            // var outList = new List<T>();
            //thisList.ForEach(outList.Add);
            //return outList;
            
            // 1-liner constructor - not flexible, but does the trick
            return new List<T>(thisList);

        }

        public static List<T> ReferenceCopy<T>(this List<T> thisList)
        {
            var newList = thisList;
            return newList;
        }

    }

    [TestFixture]
    public class TestClone
    {

        [Test]
        public void DoesThisCopy()
        {
            // Arrange
            var inList = new List<int> {1, 3, 5};

            // Act
            var outList = inList.Clone();

            // Assert
            Assert.AreEqual(inList, outList, "Lists are different");

        }

        [Test]
        public void DoesThisCopyAndNotAllowAdd()
        {
            // Arrange
            var inList = new List<int> { 1, 3, 5 };

            // Act
            var outList = inList.Clone();
            inList.Add(7);

            // Assert
            Assert.AreNotEqual(inList, outList, "Lists are same");
            Assert.AreEqual(3, outList.Count, "Outlist does not have 3 items");
            
        }

        [Test]
        public void AreReferenceObjectPointersMaintained()
        {
            
            // Arrange
            var inList = new List<Person>
                             {
                                 new Person {Name = "Jeff"}, 
                                 new Person {Name = "John"}, 
                                 new Person() {Name = "Mark"}
                             };

            // Act
            var outList = inList.Clone();
            inList[0].Name = "Jeff Fritz";

            // Assert
            Assert.AreEqual(inList[0], outList[0], "Person pointer was not maintained");
        }

        #region Test Inner Class

        public class Person
        {
            public string Name;
        }

        #endregion

    }
}