@Test
public void testMkString() {

    assertEquals("%&",     AHashSet.empty ()                    .mkString("%", "--", "&"));
    assertEquals("%a&",    AHashSet.empty ().with("a")          .mkString("%", "--", "&"));
    final String s1 = AHashSet.empty ().with("a").with("b").mkString("%", "--", "&");
    assertTrue("%b--a&".equals(s1) || "%a--b&".equals(s1));
    assertEquals("",    AHashSet.empty ()                    .mkString("#"));
    assertEquals("a",   AHashSet.empty ().with("a")          .mkString("#"));
    final String s2 = AHashSet.empty ().with("a").with("b").mkString("#");
    assertTrue("b#a".equals(s2) || "a#b".equals(s2));
}