@Test
public void testJoin() {

    final ArrayList<String> list = new ArrayList<>();
    assertEquals("", Collection.join(list, ","));
    list.add("test1");
    assertEquals("test1", Collection.join(list, ","));
    list.add("test2");
    assertEquals("test1,test2", Collection.join(list, ","));
    assertEquals("test1:sep:test2", Collection.join(list, ":sep:"));
    assertEquals("test1test2", Collection.join(list, ""));
}