### Question:
FileUtils { public static String suffix(String filename) { String fileSuffix = ""; if (StringUtils.isNotEmpty(filename)) { int lastIndex = filename.lastIndexOf('.'); if (lastIndex > 0) { fileSuffix = filename.substring(lastIndex + 1); } } return fileSuffix; } private  FileUtils(); static String suffix(String filename); static String getDownloadFilename(String filename); static String getUploadFilename(String tenantCode, String filename); static String getProcessExecDir(int projectId, int processDefineId, int processInstanceId, int taskInstanceId); static String getProcessExecDir(int projectId, int processDefineId, int processInstanceId); static String getResourceViewSuffixs(); static void createWorkDirAndUserIfAbsent(String execLocalPath, String userName); static boolean writeContent2File(String content, String filePath); static void writeStringToFile(File file, String data, Charset encoding); static void writeStringToFile(File file, String data, String encoding); static void writeStringToFile(File file, String data, Charset encoding, boolean append); static void writeStringToFile(File file, String data, String encoding, boolean append); static void writeStringToFile(File file, String data); static void writeStringToFile(File file, String data, boolean append); static FileOutputStream openOutputStream(File file); static FileOutputStream openOutputStream(File file, boolean append); static void deleteDir(String dir); static void deleteFile(String filename); static File[] getAllDir(String parentDir); static String readFile2Str(InputStream inputStream); static final Logger logger; static final String DATA_BASEDIR; static final ThreadLocal<Logger> taskLoggerThreadLocal; }### Answer:
@Test public void suffix() { Assert.assertEquals("java", FileUtils.suffix("ninfor.java")); Assert.assertEquals("", FileUtils.suffix(null)); Assert.assertEquals("", FileUtils.suffix("")); Assert.assertEquals("", FileUtils.suffix("ninfor-java")); }