### Question:
MultiplexingDocumentBuilder extends DocumentBuilder { @Override public void horizontalRule() { for (DocumentBuilder builder : builders) { builder.horizontalRule(); } } MultiplexingDocumentBuilder(DocumentBuilder... delegates); void addDocumentBuilder(DocumentBuilder delegate); @Override void acronym(String text, String definition); @Override void beginBlock(BlockType type, Attributes attributes); @Override void beginDocument(); @Override void beginHeading(int level, Attributes attributes); @Override void beginSpan(SpanType type, Attributes attributes); @Override void characters(String text); @Override void charactersUnescaped(String literal); @Override void endBlock(); @Override void endDocument(); @Override void flush(); @Override void endHeading(); @Override void endSpan(); @Override void entityReference(String entity); @Override void image(Attributes attributes, String url); @Override void imageLink(Attributes linkAttributes, Attributes imageAttributes, String href, String imageUrl); @Override void lineBreak(); @Override void horizontalRule(); @Override void link(Attributes attributes, String hrefOrHashName, String text); @Override void setLocator(Locator locator);  }### Answer:
@Test public void horizontalRule() { multiplexer.horizontalRule(); assertEvents(new HorizontalRuleEvent()); }