@Test
 public void canAppendChildElementAfterExistingElement() {
   SpinXmlElement child = XML("<child/>");
   SpinXmlElement date = element.childElement("date");
   element.appendAfter(child, date);
   SpinXmlElement insertedElement = element.childElements().get(1);
   assertThat(insertedElement.name()).isEqualTo("child");
 }
 @Test
 public void canAppendChildElementAfterLastChildElement() {
   SpinXmlElement child = XML("<child/>");
   int childCount = element.childElements().size();
   SpinXmlElement lastChildElement = element.childElements().get(childCount - 1);
   element.appendAfter(child, lastChildElement);
   SpinXmlElement insertedElement = element.childElements().get(childCount);
   assertThat(insertedElement.name()).isEqualTo("child");
 }
 @Test(expected = SpinXmlElementException.class)
 public void cannotAppendChildElementAfterNonChildElement() {
   SpinXmlElement child = XML("<child/>");
   element.appendAfter(child, child);
 }