### Question:
StringUtil { public static String join(Collection strings, String sep) { return join(strings.iterator(), sep); }  static String join(Collection strings, String sep); static String join(Iterator strings, String sep); static String padding(int width); static boolean isBlank(String string); static boolean isNumeric(String string); static boolean isWhitespace(int c); static boolean isActuallyWhitespace(int c); static String normaliseWhitespace(String string); static void appendNormalisedWhitespace(StringBuilder accum, String string, boolean stripLeading); static boolean in(String needle, String... haystack); static boolean inSorted(String needle, String[] haystack); static URL resolve(URL base, String relUrl); static String resolve(final String baseUrl, final String relUrl); static StringBuilder stringBuilder();  }### Answer:
@Test public void join() { assertEquals("", StringUtil.join(Arrays.asList(""), " ")); assertEquals("one", StringUtil.join(Arrays.asList("one"), " ")); assertEquals("one two three", StringUtil.join(Arrays.asList("one", "two", "three"), " ")); }