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How can I pass a List<T> to another List of type that T implements
public interface IRefDataItem
{
    int RefID { get; set; }
string Code { get; set; }
}

public class RACodeItem : IRefDataItem
{
    public int RefID { get; set; }
    public string Code { get; set; }
}

List<IRefDataItem> codes = GetRACodes( ); //GetRACodes returns List of RACodeItem

public interface ITest
{
}

public class Test1 : ITest
{
}

public class Test2 : ITest
{ }


static void Main(string[] args)
{
    List<ITest> list = new List<Test1>();

    list.Add(new Test1());
    list.Add(new Test2());

}