C#

start stopwatch
for (onethousand times) Panel.Refresh
stop stopwatch

public void RunTimingTest() {
    Form f=new Form();
    Button btn=new Button();
    btn.Text="Start";
    btn.Click+=new EventHandler(btn_Click);
    btn.Bounds=new Rectangle(20, 20, 200, 40);
    f.Controls.Add(btn);
    lbl=new System.Windows.Forms.Label();
    lbl.Bounds=new Rectangle(20, 80, 400, 30);
    f.Controls.Add(lbl);
    p=new MyPanel();
    p.Bounds=new Rectangle(20, 150, 200, 100);
    p.BackColor=Color.Yellow;
    f.Controls.Add(p);
    f.Show();
}

void btn_Click(object sender, EventArgs e) {
    p.Count=0;
    lbl.Text="";
    Stopwatch sw=new Stopwatch();
    sw.Start();
    int n=100*r.Next(1, 10);
    for (int i=0; i<n; i++) {
        p.Text="MyPanel "+i.ToString();
        p.Refresh();
    }
    sw.Stop();
    lbl.Text="Did "+p.Count+" paints in "+sw.ElapsedMilliseconds+" msec";
}

public class MyPanel : Panel {
    public int Count;
    public string Text;

    protected override void OnPaint(PaintEventArgs e) {
        Count++;
        base.OnPaint(e);
        e.Graphics.DrawString(Text, Font, Brushes.Black, new Point(20, 20));
    }
}