### Question:
NodeToElementWalker implements Walker<N> { @Override public void onEmpty() { delegateWalker.onEmpty(); } NodeToElementWalker(Walker<E> delegateWalker); @Override void onEmpty(); @Override boolean onNext(N node); @Override void onCompleted();  }### Answer:
@Test public void onEmpty() { final NodeToElementWalker<String, MutableSettableStructuredNode<String>> elementWalker = new NodeToElementWalker<>(walker); elementWalker.onEmpty(); Mockito.verify(walker).onEmpty(); }