### Question:
ListUtil { public static String join(Collection c) { return join(c, ", "); }  static String join(Collection c); static String join(Collection c, String join);  }### Answer:
@Test public void shouldJoinAListUsingComma(){ ArrayList<String> list = new ArrayList<String>(); list.add("a"); list.add("b"); list.add("c"); assertThat(ListUtil.join(list), is("a, b, c")); }
@Test public void shouldJoinAListUsingSpecifiedSeparator(){ ArrayList<String> list = new ArrayList<String>(); list.add("a"); list.add("b"); list.add("c"); assertThat(ListUtil.join(list, " "), is("a b c")); }