java – How should I test this method with mockito?

Method in class of service:

@Override
@Transactional (readOnly = true)
public collection searchAccounts (String partOfName) {
Collection accounts = accountDao.getAll ();
CollectionUtils.filter (accounts, account ->
account.getName (). toLowerCase (). contains (partOfName.toLowerCase ()) ||
account.getSurname (). toLowerCase (). equalsIgnoreCase (partOfName.toLowerCase ()));
to render the accounts;
}

I do not understand what I have to do with CollectionUtils.filter. to make fun of that too?
Now, I have this in test class:

@Test
public void searchAccountsByPartOfName () throws ParseException {
service.searchAccounts ("test");
verify (accountDao, times (1)). getAll ();
}