### Question:
Util { public static boolean isIdentifier(String id) { return ID_PATTERN.matcher(id).matches(); }  static void assertEquals(String expected, String actual); static String toString(int tag); static int fromString(String s); static String pidToString(byte[] libraryPersistentId); static String toUrl(String p); static boolean isIdentifier(String id);  }### Answer:
@Test public void isPlausibleIdentifier() throws UnsupportedEncodingException { assertTrue("Letters form a valid identifier", Util.isIdentifier("test")); assertTrue("Letters form a valid identifier", Util.isIdentifier("0123")); assertFalse("Non-alphanumeric characters are not a valid identifer", Util.isIdentifier("xÄ½")); assertFalse("The empty string is not a valid identifier", Util.isIdentifier("")); }