Use assertIsNone instead of assertEqual(None, ***)

Instead of using assertEqual(None, ***), developers should
use assertIsNone(***) to have more clear messages in case of failure.

Closes-Bug: #1510006
Change-Id: Ib3d09ed651877569a9b940da97662489885f18e9

HACKING.rst

@@ -9,4 +9,6 @@ Magnum Specific Commandments
 ----------------------------
 
 - [M301] policy.enforce_wsgi decorator must be the first decorator on a method.
+- [M318] Change assertEqual(A, None) or assertEqual(None, A) by optimal assert
+  like assertIsNone(A)
 - [M322] Method's default argument shouldn't be mutable.

magnum/hacking/checks.py

@@ -33,6 +33,10 @@ Guidelines for writing new hacking checks
 enforce_re = re.compile(r"@policy.enforce_wsgi*")
 decorator_re = re.compile(r"@.*")
 mutable_default_args = re.compile(r"^\s*def .+\((.+=\{\}|.+=\[\])")
+asse_equal_end_with_none_re = re.compile(
+    r"(.)*assertEqual\((\w|\.|\'|\"|\[|\])+, None\)")
+asse_equal_start_with_none_re = re.compile(
+    r"(.)*assertEqual\(None, (\w|\.|\'|\"|\[|\])+\)")
 
 
 def check_policy_enforce_decorator(logical_line,
@@ -45,6 +49,19 @@ def check_policy_enforce_decorator(logical_line,
         yield(0, msg)
 
 
+def assert_equal_none(logical_line):
+    """Check for assertEqual(A, None) or assertEqual(None, A) sentences
+
+    M318
+    """
+    msg = ("M318: assertEqual(A, None) or assertEqual(None, A) "
+           "sentences not allowed")
+    res = (asse_equal_start_with_none_re.match(logical_line) or
+           asse_equal_end_with_none_re.match(logical_line))
+    if res:
+        yield (0, msg)
+
+
 def no_mutable_default_args(logical_line):
     msg = "M322: Method's default argument shouldn't be mutable!"
     if mutable_default_args.match(logical_line):
@@ -54,3 +71,4 @@ def no_mutable_default_args(logical_line):
 def factory(register):
     register(check_policy_enforce_decorator)
     register(no_mutable_default_args)
+    register(assert_equal_none)

magnum/tests/unit/common/test_utils.py

@@ -118,8 +118,8 @@ class UtilsTestCase(base.TestCase):
                           utils.get_ip_version, 'x.x.x.x')
 
     def test_convert_to_list_dict(self):
-        self.assertEqual(None, utils.convert_to_list_dict(None, 'fred'))
-        self.assertEqual(None, utils.convert_to_list_dict('', 'fred'))
+        self.assertIsNone(utils.convert_to_list_dict(None, 'fred'))
+        self.assertIsNone(utils.convert_to_list_dict('', 'fred'))
         self.assertEqual([{'fred': 'list'}],
                          utils.convert_to_list_dict('list', 'fred'))
         self.assertEqual([{'fred': 'first'}, {'fred': 'second'}],

magnum/tests/unit/test_hacking.py

@@ -86,6 +86,16 @@ class HackingTestCase(base.TestCase):
         self._assert_has_errors(code, checks.check_policy_enforce_decorator,
                                 expected_errors=[(2, 0, "M301")])
 
+    def test_assert_equal_none(self):
+        self.assertEqual(len(list(checks.assert_equal_none(
+            "self.assertEqual(A, None)"))), 1)
+
+        self.assertEqual(len(list(checks.assert_equal_none(
+            "self.assertEqual(None, A)"))), 1)
+
+        self.assertEqual(
+            len(list(checks.assert_equal_none("self.assertIsNone()"))), 0)
+
     def test_no_mutable_default_args(self):
         self.assertEqual(1, len(list(checks.no_mutable_default_args(
             "def get_info_from_bdm(virt_type, bdm, mapping=[])"))))