### Question:
IndexResultSet extends TreeSet<IndexItem> { @Override public boolean addAll(Collection<? extends IndexItem> c) { boolean modified=false; for(IndexItem item: c) {modified=modified|add(item);} return modified; }  boolean contains(String uri); boolean contains(IndexItem item); @Override boolean contains(Object o); IndexItem get(String uri); IndexItem get(IndexItem item); @Override boolean add(IndexItem item); @Synchronized boolean remove(IndexItem item); @Override @Synchronized boolean remove(Object o); @Override boolean removeAll(Collection<?> c); @Override void clear(); @Override boolean addAll(Collection<? extends IndexItem> c); boolean retainAll(Collection<?> c); @Override Iterator<IndexItem> iterator();  }### Answer:
@Test public void testAddAll() { IndexResultSet test = new IndexResultSet(); test.addAll(cities); assertTrue(test.contains(leipzig2)); assertTrue(test.contains(berlin)); assertTrue(test.contains(dresden2)); }