### Question:
UserList { public static UserList ofCommonUsers(List<User> users) { List<PoulpeUser> poulpeUsers = new ArrayList<PoulpeUser>(); for (User user : users) { poulpeUsers.add((PoulpeUser) user); } return new UserList(poulpeUsers); } UserList(PoulpeUser... users);  UserList(List<PoulpeUser> users); static UserList ofCommonUsers(List<User> users); boolean isEmpty(); List<PoulpeUser> getUsers();  }### Answer:
@Test(expectedExceptions = ClassCastException.class) public void ofCommonUsersShouldThrowIfUsersAreNotCommon() throws Exception { UserList.ofCommonUsers(Arrays.asList(new User("", "", "", ""))); }