Remove reliance on create_engine() from TestsExceptionFilter

As we are continuing to add functionality to create_engine()
which in some cases means that backend-specific SQL is
emitted on connect, the practice of repurposing a
SQLite or other engine to act like another one for the
purposes of a test is becoming less feasible.   Here,
TestsExceptionFilter is altered to not rely upon the full
session.create_engine() process for unit tests, instead
calling upon just those listeners being tested.

Change-Id: I0ece42f956c59eab7a6cb86419d8d359250d5e71

tests/sqlalchemy/test_exc_filters.py

@@ -16,18 +16,20 @@ import contextlib
 import itertools
 
 import mock
+from oslotest import base as oslo_test_base
 import six
 import sqlalchemy as sqla
 from sqlalchemy.orm import mapper
 
 from oslo.db import exception
+from oslo.db.sqlalchemy import exc_filters
 from oslo.db.sqlalchemy import session
 from oslo.db.sqlalchemy import test_base
 
 _TABLE_NAME = '__tmp__test__tmp__'
 
 
-class TestsExceptionFilter(test_base.DbTestCase):
+class TestsExceptionFilter(oslo_test_base.BaseTestCase):
 
     class Error(Exception):
         """DBAPI base error.
@@ -61,6 +63,13 @@ class TestsExceptionFilter(test_base.DbTestCase):
 
         """
 
+    def setUp(self):
+        super(TestsExceptionFilter, self).setUp()
+        self.engine = sqla.create_engine("sqlite://")
+        exc_filters.register_engine(self.engine)
+        sqla.event.listen(self.engine, "begin", session._begin_ping_listener)
+        self.engine.connect().close()  # initialize
+
     @contextlib.contextmanager
     def _dbapi_fixture(self, dialect_name):
         engine = self.engine