### Question:
DefaultTreeWalker implements TreeWalker<E> { @Override public void onNodeChildrenCompleted(E node) { }  @Override void onStarted(); @Override void onNode(E node); @Override void onNodeChildrenStarted(E node); @Override void onNodeChildrenRemaining(E node); @Override void onNodeChildrenCompleted(E node); @Override void onNodeNoChildren(E node); @Override void onCompleted();  }### Answer:
@Test public void testOnNodeChildrenCompleted() throws Exception { WALKER.onNodeChildrenCompleted(null); }