### Question:
ConcurrentLinkedDistinctQueue extends ConcurrentLinkedQueue<E> { @Override public synchronized boolean addAll(Collection<? extends E> c) { removeAll(c); return super.addAll(c); }  synchronized boolean add(E e); @Override synchronized boolean addAll(Collection<? extends E> c);  }### Answer:
@Test public void testAddAll() { List<String> other = new ArrayList<>(); other.add("one"); other.add("one"); other.add("two"); other.add("two"); testee.addAll(other); assertListContainsOnly("one", "two"); }