### Question:
RetractElement implements ExtensionElement { @Override public XmlStringBuilder toXML(XmlEnvironment xmlEnvironment) { return new XmlStringBuilder(this).closeEmptyElement(); }  @Override String getNamespace(); @Override String getElementName(); @Override XmlStringBuilder toXML(XmlEnvironment xmlEnvironment); static final String NAMESPACE; static final String ELEMENT; }### Answer:
@Test public void serializationTest() { RetractElement retractElement = new RetractElement(); String expectedXml = "<retract xmlns='urn:xmpp:message-retract:0'/>"; assertXmlSimilar(expectedXml, retractElement.toXML()); }