Add hacking rule for assertEqual(None, *)

Several bugs have been raised and fixed to convert
assertEqual(None, *) with assertIsNone in tests.

Install a hacking rule to prevent new occurrences of
this problem.

Change-Id: Ib157f911e2f6a90d21c3886b3139f9b109962052

HACKING.rst

@@ -8,6 +8,8 @@ Manila Style Commandments
 
 Manila Specific Commandments
 ----------------------------
+
+- [M312] Use assertIsNone(...) instead of assertEqual(None, ...).
 - [M313] Use assertTrue(...) rather than assertEqual(True, ...).
 - [M319] Validate that debug level logs are not translated.
 - [M323] Ensure that the _() function is explicitly imported to ensure proper translations.

manila/hacking/checks.py

@@ -56,8 +56,8 @@ custom_underscore_check = re.compile(r"(.)*_\s*=\s*(.)*")
 oslo_namespace_imports = re.compile(r"from[\s]*oslo[.](.*)")
 dict_constructor_with_list_copy_re = re.compile(r".*\bdict\((\[)?(\(|\[)")
 assert_no_xrange_re = re.compile(r"\s*xrange\s*\(")
-assert_True = re.compile(
-    r".*assertEqual\(True, .*\)")
+assert_True = re.compile(r".*assertEqual\(True, .*\)")
+assert_None = re.compile(r".*assertEqual\(None, .*\)")
 
 
 class BaseASTChecker(ast.NodeVisitor):
@@ -258,6 +258,13 @@ def validate_assertTrue(logical_line):
         yield(0, msg)
 
 
+def validate_assertIsNone(logical_line):
+    if re.match(assert_None, logical_line):
+        msg = ("M312: Unit tests should use assertIsNone(value) instead"
+               " of using assertEqual(None, value).")
+        yield(0, msg)
+
+
 def factory(register):
     register(validate_log_translations)
     register(check_explicit_underscore_import)
@@ -268,3 +275,4 @@ def factory(register):
     register(dict_constructor_with_list_copy)
     register(no_xrange)
     register(validate_assertTrue)
+    register(validate_assertIsNone)

manila/tests/test_hacking.py

@@ -250,3 +250,10 @@ class HackingTestCase(test.TestCase):
             "assertTrue(True)"))))
         self.assertEqual(1, len(list(checks.validate_assertTrue(
             "assertEqual(True, %s)" % test_value))))
+
+    def test_validate_assertIsNone(self):
+        test_value = None
+        self.assertEqual(0, len(list(checks.validate_assertIsNone(
+            "assertIsNone(None)"))))
+        self.assertEqual(1, len(list(checks.validate_assertIsNone(
+            "assertEqual(None, %s)" % test_value))))