FileLoader implements Serializable { public String loadData() { String dataFileName = this.fileName; try (BufferedReader br = new BufferedReader(new FileReader(new File(dataFileName)))) { StringBuilder sb = new StringBuilder(); String line; while ((line = br.readLine()) != null) { sb.append(line).append('\n'); } this.loaded = true; return sb.toString(); } catch (Exception e) { LOGGER.error("File {} does not exist", dataFileName); } return null; }  String loadData(); void setFileName(String fileName); String getFileName(); boolean fileExists(); boolean isLoaded();  }
@Test public void testLoadData() throws Exception { final FileLoader fileLoader = new FileLoader(); fileLoader.setFileName("non-existing-file"); assertNull(fileLoader.loadData()); }