### Question:
MimeType { static String getExtension(final String fileName) { int ix = fileName.lastIndexOf('.'); if (ix == -1) { return ""; } return fileName.substring(ix); }  static String get(String fileExtension, final String defaultValue); static String getMimeTypeOfFile(final String fileName); static String getMimeTypeOfFile(final String fileName, final String defaultValue);  }### Answer:
@Test public void testGetExtension() { assertEquals(".js", MimeType.getExtension("aa.js")); assertEquals(".JS", MimeType.getExtension("aa.JS")); assertEquals(".htm", MimeType.getExtension("aa.htm")); assertEquals("", MimeType.getExtension("aa")); }