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