public void RectExtensions2() { Rect a = new Rect(10, 20, 30, 40); Assert.AreEqual(20, a.Add_X(10).x); Assert.AreEqual(0, a.Add_X(-10).x); Assert.AreEqual(40, a.Add_Y(20).y); Assert.AreEqual(60, a.Add_Width(30).width); Assert.AreEqual(80, a.Add_Height(40).height); }