tests: Enable SQLAlchemy 2.0 deprecation warnings

Well, sort of. We enable them but immediately filter out the ones we're
actually seeing, the rationale being that we can address these in a
piecemeal fashion without the risk of introducing new issues.

There's a bit more to be done here. However, the work done in oslo.db
and other projects [1] should provide a guide for how to resolve the
outstanding issues.

[1] https://review.opendev.org/q/topic:sqlalchemy-20

Change-Id: I36a79377016a6913f2c63cac4c820ad8342ffbf6
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

barbican/tests/fixture.py

@@ -18,6 +18,7 @@ import fixtures
 from oslo_db.sqlalchemy import session
 from oslo_utils import timeutils
 import sqlalchemy as sa
+from sqlalchemy import exc as sqla_exc
 
 from barbican.model import models
 
@@ -175,6 +176,44 @@ class WarningsFixture(fixtures.Fixture):
 
         warnings.simplefilter('once', DeprecationWarning)
 
+        # Enable deprecation warnings for barbican itself to capture upcoming
+        # SQLAlchemy changes
+
+        warnings.filterwarnings(
+            'ignore',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'error',
+            module='barbican',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='barbican',
+            message=r'".*" object is being merged into a Session along .*',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='barbican',
+            message=r'The legacy calling style of select\(\) .*',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        # Enable general SQLAlchemy warnings also to ensure we're not doing
+        # silly stuff. It's possible that we'll need to filter things out here
+        # with future SQLAlchemy versions, but that's a good thing
+
+        warnings.filterwarnings(
+            'error',
+            module='barbican',
+            category=sqla_exc.SAWarning,
+        )
+
         self.addCleanup(self._reset_warning_filters)
 
     def _reset_warning_filters(self):

tox.ini

@@ -6,6 +6,8 @@ envlist = py38,py39,pep8,docs
 setenv =
   PYTHON=coverage run --source barbican --parallel-mode
   PYTHONDONTWRITEBYTECODE=1
+# TODO(stephenfin): Remove once we bump our upper-constraint to SQLAlchemy 2.0
+  SQLALCHEMY_WARN_20=1
 usedevelop = True
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}