Dynamic dispatch + printing of BDD steps

DynamicBDDBase.cs

// Complementary to http://gist.github.com/406014. Just swap your BDD<T> base class for DBDD
// Also licensed under MSPL/FreeBSD/ISC 

    public abstract class DBDD
    {
        public readonly dynamic Given;
        public readonly dynamic When;
        public readonly dynamic Then;
        public readonly dynamic And;

        protected DBDD()
        {
            Given = new PrintingDispatcher("Given", this);
            When = new PrintingDispatcher("When", this);
            Then = new PrintingDispatcher("Then", this);
            And = new PrintingDispatcher("And", this);
        }
    }

    class PrintingDispatcher : DynamicObject
    {
        readonly string prefix;
        readonly object source;

        public PrintingDispatcher(string prefix, object source)
        {
            this.prefix = prefix;
            this.source = source;
        }

        public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result)
        {
            MethodInfo methodInfo = source.GetType().GetMethod(binder.Name, BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.FlattenHierarchy);

            Debug.WriteLine("{0} {1} ({2})", prefix, binder.Name.Replace('_', ' '), String.Join(", ", args));
            if (methodInfo != null)
            {
                methodInfo.Invoke(source, args);
            }
            else
            {
                const string format = @"You need a method like:

    void {0}()
    {{
       throw new NotImplementedException();
    }}";
                throw new NotImplementedException(string.Format(format, binder.Name));
            }
            result = null;
            return true;
        }
    }