### Question:
StringUtils { public static String setToStr(Set<String> stringSet, String delimiter) { return setToStr(stringSet, delimiter, EMPTY_STRING); }  static boolean isEmpty(String str); static boolean isSameStr(String a, String b); static String setToStr(Set<String> stringSet, String delimiter); static String setToStr(Set<String> stringSet, String delimiter, String defaultRet); static Set<String> strToSet(String str, String delimiter); static List<String> strToList(String str, String delimiter); static boolean startWithToLowerCase(String thisString, String anotherString); static final String EMPTY_STRING; static final int CHAR_A; static final int CHAR_Z; static final int CASE_GAP; }### Answer:
@Test @SuppressWarnings("unchecked") public void testListToStr() { Assert.assertTrue("".equals(StringUtils.setToStr(null, ","))); Assert.assertTrue("".equals(StringUtils.setToStr(Collections.<String> emptySet(), ","))); Assert.assertTrue("ast".equals(StringUtils.setToStr(Collections.singleton("ast"), "&&"))); LinkedHashSet linkedHashSet = new LinkedHashSet(); linkedHashSet.add("ab"); linkedHashSet.add(" ba "); Assert.assertTrue("ab,ba".equals(StringUtils.setToStr(linkedHashSet, ","))); linkedHashSet.add("cb"); Assert.assertTrue("ab&&ba&&cb".equals(StringUtils.setToStr(linkedHashSet, "&&"))); Assert.assertTrue("abbacb".equals(StringUtils.setToStr(linkedHashSet, ""))); }