Use public interfaces of pep8 for hacking

Rather than using mock and pep8 internals, we can use
public interfaces of pep8 to register our custom
hacking checks. Further, if pep8 isn't present for testing purposes,
we can simply use pycodestyle. Many distributions are shipping the
latter these days instead of pep8.

Closes-Bug: 1652458

Co-Authored-By: Ian Cordasco <graffatcolmingov@gmail.com>
Change-Id: Ica719703c54a295d10ea800467b25a5d0f65348a
Signed-off-by: Adam Williamson <awilliam@redhat.com>

keystone/tests/unit/test_hacking_checks.py

@@ -12,8 +12,13 @@
 
 import textwrap
 
-import mock
-import pep8
+try:
+    import pep8
+except ImportError:
+    # NTOE(stevemar): pycodestyle is not yet in global-requirements, but
+    # packagers have begun pycodestyle (the renamed version of pep8)
+    # See: https://github.com/PyCQA/pycodestyle/issues/466
+    import pycodestyle as pep8
 
 from keystone.tests.hacking import checks
 from keystone.tests import unit
@@ -35,16 +40,15 @@ class BaseStyleCheck(unit.BaseTestCase):
     def get_fixture(self):
         return hacking_fixtures.HackingCode()
 
-    # We are patching pep8 so that only the check under test is actually
-    # installed.
-    @mock.patch('pep8._checks',
-                {'physical_line': {}, 'logical_line': {}, 'tree': {}})
     def run_check(self, code):
         pep8.register_check(self.get_checker())
 
         lines = textwrap.dedent(code).strip().splitlines(True)
 
-        checker = pep8.Checker(lines=lines)
+        # Load all keystone hacking checks, they are of the form Kddd,
+        # where ddd can from range from 000-999
+        guide = pep8.StyleGuide(select='K')
+        checker = pep8.Checker(lines=lines, options=guide.options)
         checker.check_all()
         checker.report._deferred_print.sort()
         return checker.report._deferred_print