Enhanced fixtures for enginefacade-based provisioning

The original idea of enginefacade was that applications
would call upon the global _TransactionContextManager
given in oslo_db.sqlalchemy.enginefacade.  However, as it
turns out, virtually no Openstack projects seem to be
using that technique, and instead, everyone is creating
their own ad-hoc _TransactionContextManager objects
and usually establishing it as a module-level global.
Nova has two of them.

Additionally, projects add configuration to these
enginefacades (which IS part of the original idea), and
this configuration in some cases is necessary to be present
for tests that run as well, a key example being the
sqlite_fks flag.   The original DbFixture integration
provided no way of reusing this configuration.

Finally, projects very much tend to use custom fixtures
in order to define their database communication.
Test classes themselves don't really make use of
oslo_db's DbTestCase anymore.

This patch introduces a modernized fixture system
which, in conjunction with the recent provisioning
patch, addresses these use cases.   Applications will typically
create their own subclasses of these fixtures up front
to suit the various testing cases they have, including
SQLite fixed, SQLite ad-hoc, and opportunistic.

In order to accommodate the fixture-based flow
along with the use of testresources for opportunistic
database provisioning, a mixin class OpportunisticDbTestMixin
is still needed when a test needs to use "opportunistic"
testing in order to provide the .resources attribute.
The calculation of .resources is moved into the fixture
system, but because this attribute is consulted before
setUp(), the "opportunistic" fixture must be created
early and stored.

Closes-Bug: #1548960

Change-Id: I0163e637ffef6d45d2573ebe29b5438911d01fce

1 files changed, 5 insertions, 0 deletions

diff --git a/releasenotes/notes/new-db-fixtures-58223e3926122413.yaml b/releasenotes/notes/new-db-fixtures-58223e3926122413.yaml
new file mode 100644
index 0000000..474f505
--- /dev/null
+++ b/releasenotes/notes/new-db-fixtures-58223e3926122413.yaml
@@ -0,0 +1,5 @@
+---
+deprecations:
+  - base test classes from ``oslo_db.sqlalchemy.test_base`` are deprecated in
+    favor of new fixtures introduced in ``oslo_db.sqlalchemy.test_fixtures``
+    module