@Test
 public void defaultValueIsZero() throws Exception {
   document = new Counter(null).toHtmlDocument();
   assertEquals("0x0", document.findElementById("display").contentsAsText());
 }
 @Test
 public void containsDisplay() throws Exception {
   Element display = document.findElementById("display");
   assertEquals("Display shows wrong value", "0xff", display.contentsAsText());
 }