TypeError: exceptions must be old-style classes or derived from BaseException, not MagicMock

Question

I want to test the exception handling in my code:

def test_get_mails__exception_in_search(self):
    with mock.patch('imaplib.IMAP4', autospec=True) as imap_mock:
        imap_mock.return_value.create.return_value = ('OK', [''])
        imap_mock.return_value.search.side_effect=imap_mock.error
        self.get_mails()

But the mock library raises:

TypeError: exceptions must be old-style classes or derived from BaseException, 
not MagicMock

How can I test my code: I want imaplib.search to raise imaplib.error

Answer 1

I found a solution:

    with mock.patch('imaplib.IMAP4', autospec=True) as imap_mock:
        imap_mock.error=Exception # <----    This is needed, don't ask me why
        imap_mock.return_value.create.return_value = ('OK', [''])
        imap_mock.return_value.search.side_effect=imap_mock.error
        self.get_mails()