public void UndoTest()
{
MaskedTextBox mtb;
mtb = new MaskedTextBox();
mtb.Text = "abcdef";
Assert.AreEqual(false, mtb.CanUndo, "#A0-c");
mtb.Undo();
Assert.AreEqual("abcdef", mtb.Text, "#A1");
Assert.AreEqual(false, mtb.CanUndo, "#A1-c");
mtb.Text = "cdef";
mtb.ClearUndo();
Assert.AreEqual("cdef", mtb.Text, "#A2");
Assert.AreEqual(false, mtb.CanUndo, "#A2-c");
mtb.Dispose();
}