public void WithCancellation()
        {
            var cts = new CancellationTokenSource();
            var tk  = cts.Token;
            var opt = (CallOptions)client.AsDynamic().option;

            opt.CancellationToken.IsNot(tk);

            var change = client.WithCancellationToken(tk);

            opt = (CallOptions)change.AsDynamic().option;

            opt.CancellationToken.Is(tk);
        }