/// <summary>
/// Add in item to a collection if it does not contain the specified element by using a IEqualityComparer<>. 
/// </summary>
/// <typeparam name="T">Type of the items in a collection</typeparam>
/// <param name="collection">The collection to add  the item</param>
/// <param name="item">The item to add to the collection</param>
/// <param name="comparer">An equality comparer to compare values.</param>
/// <returns>true if the item was added to the collection; otherwise, false.</returns>
public static bool Add<T>(this ICollection<T> collection, T item, IEqualityComparer<T> comparer)
{

[TestMethod]
public void CanGetValueItemfromCollection()
{
    var col = new Collection<string> {"Hello", "World"};
    var testItem = col.GetValueItem(c => c.Equals("World"));
    Assert.AreEqual(testItem, "World");
}
 
[TestMethod]
public void CanGetReferenceItemfromCollectionByProperty()

/// <summary>
/// Find an object in a value-type collection.
/// </summary>
/// <typeparam name="T">Type of collection.</typeparam>
/// <param name="collection">The collection to search.</param>
/// <param name="isMatch">The Predicate to test to find the collection item.</param>
/// <returns>The collection item.</returns>
public static T GetValueItem<T>(this ICollection<T> collection, Predicate<T> isMatch)
{
    foreach (var item in collection)

public class Order
{
     private List<OrderLine> _orderLines;
     public IEnumerable<OrderLine> OrderLines
     {
         get { return _orderLines; }
     }
     public void AddOrderLine(OrderLine orderLine)
     {
         _orderTotal += orderLine.Total;