### Question:
ContentExtractor { public List<String> extractAll() { int numberOfPages = reader.getNumberOfPages(); List<String> txtContentList = new LinkedList<>(); for (int pageNum = 1; pageNum <= numberOfPages; pageNum++) { List<String> pageContent = getPageContent(pageNum); if (pageContent != null && !pageContent.isEmpty()) { txtContentList.addAll(pageContent); } } return txtContentList; } private  ContentExtractor();  ContentExtractor(OFDReader reader); List<String> getPageContent(int pageNum); List<String> extractAll(); void traverse(Receiver e);  }### Answer:
@Test void extractAll() throws IOException { try (OFDReader reader = new OFDReader(src)) { ContentExtractor extractor = new ContentExtractor(reader); List<String> pageContent = extractor.extractAll(); System.out.println(pageContent); assertEquals(pageContent.size(), 1); assertEquals("你好呀，OFD Reader&Writer！", pageContent.get(0)); } }