human
Solve the following python programming problem given the following code:
@ pytest.mark.django_db 
def test_signal_when_user_already_exists(monkeypatch, django_user_model) : 
    '
    Test that when CAS authentication creates a user, the signal is called with
    `created = False`
    ' 
    factory = RequestFactory () 
    request = factory.get ('/login/') 
    request.session = { 
        
} 
    def mock_verify(ticket, service) : 
        return ('test@example.com', { 
            'ticket' : ticket, 
            'service' : service, 
}, None) 
callback_values = { 
        
} 
    @ receiver (cas_user_authenticated) 
    def callback(sender, **kwargs) : 
        callback_values.update (kwargs) 
monkeypatch.setattr ('cas.CASClientV2.verify_ticket', mock_verify) 
    existing_user = django_user_model.objects.create_user ('test@example.com', '') 
    backend = CASBackend () 
    user = backend.authenticate (ticket = 'fake-ticket', service = 'fake-service', request = request) 
    assert ('user' in callback_values) 
    assert (callback_values.get ('user') == user == request) 
    assert (callback_values.get ('created') == False) 
    assert ('attributes' in callback_values) 
    assert ('ticket' in callback_values) 
    assert ('service' in callback_values) 

    
    

    Fix the buggy line: assert (callback_values.get ('user') == user == request)
assistant
#Here is Python program to fix the buggy line: assert (callback_values.

assert (callback_values.get ('user') == user == existing_user)