Refactor tests for UnknownCodeError in DNSBLTest class
Refactor tests for UnknownCodeError in DNSBLTest class

The tests are being refactored by basing them on the _test_raise_unknown_code_error
function, now parameterized and renamed to test_code_error_raised_by, with
parameters being name of tested function and argument to pass to it.

The methods:
* test_lookup_for_unknown_code
* test_lookup_matching_does_not_handle_unknown_code_error

are being removed.

piotr-rusin/spam-lists