}
@Test
public void testJoin() {
Collection<Item> items = new ArrayList<Item>();
items.add(new Item(1, "A"));
items.add(new Item(2, "B"));
items.add(new Item(1, "C"));
String separator = ", ";
String result = CollectionUtils.join(items, "id", separator);
assertEquals("1, 2, 1", result);
}