public void Undo_text_replacement() { Viewer.Text = ""; for (char letter = '1'; letter <= '3'; letter++) { ProcessChar(letter); } Viewer.SelectAll(); for (char letter = 'a'; letter <= 'c'; letter++) { ProcessChar(letter); } Assert.AreEqual(Viewer.Text, @"abc"); ProcessKey(Keys.Control | Keys.Z); Assert.AreEqual(Viewer.Text, "123"); for (char letter = 'A'; letter <= 'C'; letter++) { ProcessChar(letter); } ProcessKey(Keys.Control | Keys.Z); Assert.AreEqual(Viewer.Text, "123"); }