When doing testing, I tend to create an object mother for the items generated multiple times for specifications. Quite often these objects need to be a part of a collection. A neat way to do so is to leverage .NET params mechanism:

    public static IEnumerable<T> CreateCollection<T>(params T[] items)
    {
      return items;
    }

And usage is the following:

private static IEnumerable<IPAddress> addresses = CreateCollection(new IPAddress(123456789), new IPAddress(987654321));