Merge "fix usage of opportunistic test cases with enginefacade"

nova/tests/fixtures.py

@@ -23,6 +23,7 @@ import warnings
 
 import fixtures
 from oslo_config import cfg
+from oslo_db.sqlalchemy import enginefacade
 from oslo_messaging import conffixture as messaging_conffixture
 import six
 
@@ -476,3 +477,39 @@ class StableObjectJsonFixture(fixtures.Fixture):
 
         self.useFixture(fixtures.MonkeyPatch(
             'nova.objects.base.NovaObject.obj_to_primitive', _doit))
+
+
+class EngineFacadeFixture(fixtures.Fixture):
+    """Fixture to isolation EngineFacade during tests.
+
+    Because many elements of EngineFacade are based on globals, once
+    an engine facade has been initialized, all future code goes
+    through it. This means that the initialization of sqlite in
+    databases in our Database fixture will drive all connections to
+    sqlite. While that's fine in a production environment, during
+    testing this means we can't test againts multiple backends in the
+    same test run.
+
+    oslo.db does not yet support a reset mechanism here. This builds a
+    custom in tree engine facade fixture to handle this. Eventually
+    this will be added to oslo.db and this can be removed. Tracked by
+    https://bugs.launchpad.net/oslo.db/+bug/1548960
+
+    """
+    def __init__(self, ctx_manager, engine, sessionmaker):
+        super(EngineFacadeFixture, self).__init__()
+        self._ctx_manager = ctx_manager
+        self._engine = engine
+        self._sessionmaker = sessionmaker
+
+    def setUp(self):
+        super(EngineFacadeFixture, self).setUp()
+
+        self._existing_factory = self._ctx_manager._root_factory
+        self._ctx_manager._root_factory = enginefacade._TestTransactionFactory(
+            self._engine, self._sessionmaker, apply_global=False,
+            synchronous_reader=True)
+        self.addCleanup(self.cleanup)
+
+    def cleanup(self):
+        self._ctx_manager._root_factory = self._existing_factory