### Question:
IndexResultSet extends TreeSet<IndexItem> { @Override public void clear() { uriToItem.clear(); super.clear(); }  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 testClear() { IndexResultSet test = testSet(); test.clear(); assertTrue(test.isEmpty()); assertTrue(test.uriToItem.isEmpty()); }