### Question:
SelectedSelectionKeySet extends AbstractSet<SelectionKey> { @Override public boolean contains(Object o) { return false; } SelectedSelectionKeySet(); @Override boolean add(SelectionKey o); @Override boolean remove(Object o); @Override boolean contains(Object o); @Override int size(); @Override Iterator<SelectionKey> iterator();  }### Answer:
@Test public void contains() { SelectedSelectionKeySet set = new SelectedSelectionKeySet(); assertTrue(set.add(mockKey)); assertTrue(set.add(mockKey2)); assertFalse(set.contains(mockKey)); assertFalse(set.contains(mockKey2)); assertFalse(set.contains(mockKey3)); }