Use the :pep: tag instead of directly linking PEPs

docs/writing/tests.rst

@@ -16,7 +16,7 @@ Some general rules of testing:
   alone, and also within the test suite, regardless of the order they are called.
   The implication of this rule is that each test must be loaded with a fresh
   dataset and may have to do some cleanup afterwards. This is usually
-  handled by setUp() and tearDown() methods.
+  handled by `setUp()` and `tearDown()` methods.
 
 - Try hard to make tests that run fast. If one single test needs more than a
   few millisecond to run, development will be slowed down or the tests will not
@@ -287,7 +287,7 @@ always returns the same result (but only for the duration of the test).
     # not where the SearchForm class itself is imported from
     @mock.patch('myapp.SearchForm.search', mock_search)
     def test_new_watchlist_activities(self):
-        # get_search_results runs a search and iterates over the result 
+        # get_search_results runs a search and iterates over the result
         self.assertEqual(len(myapp.get_search_results(q="fish")), 3)
 
 Mock has many other ways you can configure it and control its behavior.