[IMP] tests: allow to add a margin on performance tests

Purpose of this commit is to avoid errors for some performance tests that
have a slightly variable number of queries. Indeed some tests in test_mail
module vary of 1 or 2 queries due to a behavior still not found that does
not seem deterministic.

This should not be considered as a real error, but should not be considered
as completely valid. This is why a margin is accepted in some tests that
will raise a warning instead of an error. This warning tells people to
check if they have increased the query counter or if it is due to a random
effect in query count.

odoo/tests/common.py

@@ -192,7 +192,7 @@ class BaseCase(TreeCase, MetaCase('DummyCase', (object,), {})):
             return self._assertRaises(exception)
 
     @contextmanager
-    def assertQueryCount(self, default=0, **counters):
+    def assertQueryCount(self, default=0, margin=0, **counters):
         """ Context manager that counts queries. It may be invoked either with
             one value, or with a set of named arguments like ``login=value``::
 
@@ -210,13 +210,17 @@ class BaseCase(TreeCase, MetaCase('DummyCase', (object,), {})):
             count0 = self.cr.sql_log_count
             yield
             count = self.cr.sql_log_count - count0
-            if not count <= expected:
-                msg = "Query count for user %s: got %d instead of %d"
-                self.fail(msg % (login, count, expected))
+            if count > (expected + margin):
+                msg = "Too much query count: user %s: got %d instead of %d (margin %s)"
+                self.fail(msg % (login, count, expected, margin))
+            elif count > expected and count <= (expected + margin):
+                logger = logging.getLogger(type(self).__module__)
+                msg = "Query count greater but still in margin : user %s: got %d instead of %d (margin %s)"
+                logger.warn(msg, login, count, expected, margin)
             elif count < expected:
                 logger = logging.getLogger(type(self).__module__)
-                msg = "Query count for user %s: got %d instead of %d"
-                logger.info(msg, login, count, expected)
+                msg = "Better query count: user %s: got %d instead of %d (margin %s)"
+                logger.info(msg, login, count, expected, margin)
         else:
             yield