### Question:
Users { public Set<String> getUserNames() { return userMap.keySet(); } Users(); int size(); User get(int index); User get(String username); Set<String> getUserNames();  }### Answer:
@Test public void testDisplayLoggedOnUsers() { MyApplication application = new MyApplication(); Users users = new Users(); Set<String> usernames = users.getUserNames(); for (String username : usernames) { application.logon(username); } application.displayUsers(); }