Issue 6877 - Only parse headers in the first line of the filter list

tests/test_parser.py

 # This file is part of Adblock Plus <https://adblockplus.org/>,
 # Copyright (C) 2006-present eyeo GmbH
 #
 # Adblock Plus is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 3 as
 # published by the Free Software Foundation.
 #
 # Adblock Plus is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
@@ skipping 142 matching lines @@
     assert line.target == 'foo:bar/baz.txt'
 
 
 def test_parse_bad_instruction():
     with pytest.raises(ParseError):
         parse_line('%foo bar%')
 
 
 def test_parse_bad_header():
     with pytest.raises(ParseError):
-        parse_line('[Adblock 1.1]')
+        parse_line('[Adblock 1.1]', mode='start')
 
 
 def test_parse_filterlist():
     result = parse_filterlist(['[Adblock Plus 1.1]',
                                '! Homepage  :  http://aaa.com/b',
                                '||example.com^',
                                '! Checksum: OaopkIiiAl77sSHk/VAWDA',
                                '! Note: bla bla'])
 
     assert next(result) == Header('Adblock Plus 1.1')
     assert next(result) == Metadata('Homepage', 'http://aaa.com/b')
     assert next(result).type == 'filter'
     assert next(result) == Metadata('Checksum', 'OaopkIiiAl77sSHk/VAWDA')
     assert next(result).type == 'comment'
 
     with pytest.raises(StopIteration):
         next(result)
 
 
 def test_exception_timing():
     result = parse_filterlist(['! good line', '%bad line%'])
     assert next(result) == Comment('good line')
     with pytest.raises(ParseError):
         next(result)
 
 
 def test_parse_line_bytes():
     line = parse_line(b'! \xc3\xbc')
     assert line.text == '\xfc'