HtmlSubmitInput button = (HtmlSubmitInput) list.get(0);
list = getAllElementsOfGivenClass(page, null, HtmlSelect.class);
HtmlSelect options = (HtmlSelect) list.get(0);
String chosen [] = {"2", "3"};
options.fakeSelectedAttribute(chosen);
page = (HtmlPage) button.click();
ResourceBundle messages = ResourceBundle.getBundle(
"javax.faces.Messages");
String message = messages.getString("javax.faces.component.UISelectMany.INVALID");
// it does not have a validation message