Adjust SAVEPOINT cause test for SQLA 1.1

SQLAlchemy 1.1 has repaired some of the failure modes
for Session.rollback(), including the MySQL case where the savepoint
identifier gets lost, such that the Session is in a more usable
state than before.  A side effect of this is that the test
here in oslo.db only hits a single error handler, not two.

SQLAlchemy upstream is described at:

https://docs.sqlalchemy.org/en/latest/changelog/migration_11.html#improved-session-state-when-a-savepoint-is-cancelled-by-the-database

Change-Id: I324f288701e9ffd241de638e0e0419dc8d9c1264

2 files changed, 29 insertions, 13 deletions

diff --git a/oslo_db/sqlalchemy/compat/utils.py b/oslo_db/sqlalchemy/compat/utils.py
index 8ebffcc..e34e70f 100644
--- a/oslo_db/sqlalchemy/compat/utils.py
+++ b/oslo_db/sqlalchemy/compat/utils.py
@@ -19,6 +19,7 @@ SQLA_VERSION = tuple(
     for num in sqlalchemy.__version__.split(".")
 )
 
+sqla_110 = SQLA_VERSION >= (1, 1, 0)
 sqla_100 = SQLA_VERSION >= (1, 0, 0)
 sqla_097 = SQLA_VERSION >= (0, 9, 7)
 sqla_094 = SQLA_VERSION >= (0, 9, 4)
diff --git a/oslo_db/tests/sqlalchemy/test_exc_filters.py b/oslo_db/tests/sqlalchemy/test_exc_filters.py
index a45214d..8e62a77 100644
--- a/oslo_db/tests/sqlalchemy/test_exc_filters.py
+++ b/oslo_db/tests/sqlalchemy/test_exc_filters.py
@@ -28,6 +28,7 @@ from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import mapper
 
 from oslo_db import exception
+from oslo_db.sqlalchemy.compat import utils as compat_utils
 from oslo_db.sqlalchemy import engines
 from oslo_db.sqlalchemy import exc_filters
 from oslo_db.tests.sqlalchemy import base as test_base
@@ -666,22 +667,36 @@ class TestExceptionCauseMySQLSavepoint(test_base.MySQLOpportunisticTestCase):
                 # from the "with session.begin_nested()"
                 except exception.DBError as dbe_inner:
 
-                    # first "cause" is the failed SAVEPOINT rollback
-                    # from inside of flush(), when it fails
-                    self.assertTrue(
-                        isinstance(
-                            dbe_inner.cause,
-                            exception.DBError
+                    if not compat_utils.sqla_110:
+                        # first "cause" is the failed SAVEPOINT rollback
+                        # from inside of flush(), when it fails
+                        self.assertTrue(
+                            isinstance(
+                                dbe_inner.cause,
+                                exception.DBError
+                            )
                         )
-                    )
 
-                    # second "cause" is then the actual DB duplicate
-                    self.assertTrue(
-                        isinstance(
-                            dbe_inner.cause.cause,
-                            exception.DBDuplicateEntry
+                        # second "cause" is then the actual DB duplicate
+                        self.assertTrue(
+                            isinstance(
+                                dbe_inner.cause.cause,
+                                exception.DBDuplicateEntry
+                            )
                         )
-                    )
+                    else:
+                        # in SQLA 1.1, the rollback() method of Session
+                        # catches the error and repairs the state of the
+                        # session even though the SAVEPOINT was lost;
+                        # the net result here is that one exception is thrown
+                        # instead of two.  This is SQLAlchemy ticket #3680
+                        self.assertTrue(
+                            isinstance(
+                                dbe_inner.cause,
+                                exception.DBDuplicateEntry
+                            )
+                        )
+
         except exception.DBError as dbe_outer:
             self.assertTrue(
                 isinstance(