human
Solve the following python programming problem given the following code:
@ patch ('rerun.rerun.is_ignorable') 
@ patch ('rerun.rerun.has_file_changed') 
@ patch ('rerun.rerun.os') 
def test_get_changed_files(self, mock_os, mock_changed, mock_ignorable) : 
    def fake_has_changed(relname) : 
        return (relname in ['root/f', 'root/l', 'root/s']) 
mock_changed.side_effect = <MASK> 
    def fake_is_ignorable(relname, _) : 
        return (relname in ['root/l']) 
mock_ignorable.side_effect = fake_is_ignorable 
    mock_os.walk.return_value = [('root', list ('dirs'), list ('files'))] 
    mock_os.path.join = os.path.join 
    actual = get_changed_files ([]) 
    self.assertEqual (actual, [os.path.join ('root', 'f'), os.path.join ('root', 's')]) 
    self.assertEqual (mock_changed.call_count, 5) 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: actual, mock_changed, self, fake_is_ignorable, mock_ignorable, mock_os
assistant
#Here is a proper replacement for <MASK>.
def fake_has_changed(