### Question:
AbstractSettableNode implements OpenSettableNode<E, N> { @Override public E setElement(E element) { return elementReference.getAndSet(element); } AbstractSettableNode(E element); @Override E getElement(); @Override E setElement(E element);  }### Answer:
@Test public void setElement() { assertEquals("a", node.setElement("b")); assertEquals("b", node.getElement()); }