### Question:
DiffDocumentIterator extends AbstractDocumentIterator<DiffDocumentIterator.Action> { @Override public void setRootReference(EntityReference rootReference) { previous.setRootReference(rootReference); next.setRootReference(rootReference); } DiffDocumentIterator(DocumentIterator<T> previous, DocumentIterator<T> next); @Override void setRootReference(EntityReference rootReference); @Override boolean hasNext(); @Override Pair<DocumentReference, Action> next(); @Override long size();  }### Answer:
@SuppressWarnings("unchecked") @Test public void setRootReference() { DocumentIterator<String> previous = mock(DocumentIterator.class, "previous"); DocumentIterator<String> next = mock(DocumentIterator.class, "next"); DiffDocumentIterator<String> iterator = new DiffDocumentIterator<String>(previous, next); WikiReference rootReference = new WikiReference("foo"); iterator.setRootReference(rootReference); verify(previous).setRootReference(rootReference); verify(next).setRootReference(rootReference); }