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 lot more to be done here. However, the work done in oslo.db
[1] should provide a guide for how to resolve the outstanding issues.

[1] https://review.opendev.org/q/topic:"sqlalchemy-20"+project:openstack/oslo.db

Change-Id: I9e8d3e3a82c51c3c008ef7380f2f619ed492205e
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

cinder/tests/fixtures.py

@@ -124,7 +124,7 @@ class WarningsFixture(fixtures.Fixture):
     """Filters out warnings during test runs."""
 
     def setUp(self):
-        super(WarningsFixture, self).setUp()
+        super().setUp()
 
         self._original_warning_filters = warnings.filters[:]
 
@@ -166,18 +166,93 @@ class WarningsFixture(fixtures.Fixture):
             module='cinder',
         )
 
+        warnings.filterwarnings(
+            'ignore',
+            message='Policy ".*":".*" was deprecated in ',
+            module='oslo_policy',
+            category=UserWarning,
+        )
+
+        # Enable deprecation warnings for cinder itself to capture upcoming
+        # SQLAlchemy changes
+
         warnings.filterwarnings(
             'ignore',
             category=sqla_exc.SADeprecationWarning,
         )
 
-        # TODO: Make this an error and filter out individual failures
         warnings.filterwarnings(
-            'once',
+            'error',
             module='cinder',
             category=sqla_exc.SADeprecationWarning,
         )
 
+        # ...but filter everything out until we get around to fixing them
+        # TODO: Fix all of these
+
+        warnings.filterwarnings(
+            'ignore',
+            module='cinder',
+            message=r'The "whens" argument to case\(\) is now passed using ',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='cinder',
+            message=r'The "whens" argument to case\(\), when referring to ',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='cinder',
+            message='Using strings to indicate column or relationship paths ',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='cinder',
+            message='Using strings to indicate relationship names in Query',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='cinder',
+            message='The current statement is being autocommitted using ',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='cinder',
+            message=r'The SelectBase.as_scalar\(\) method is deprecated ',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='cinder',
+            message=r'Passing a string to Connection.execute\(\) is ',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='cinder',
+            message='The Session.begin.subtransactions flag is deprecated ',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
+        warnings.filterwarnings(
+            'ignore',
+            module='cinder',
+            message=r'The legacy calling style of select\(\) is deprecated ',
+            category=sqla_exc.SADeprecationWarning,
+        )
+
         self.addCleanup(self._reset_warning_filters)
 
     def _reset_warning_filters(self):

tox.ini

@@ -10,16 +10,20 @@ ignore_basepython_conflict=true
 
 [testenv]
 basepython = python3
-setenv = VIRTUAL_ENV={envdir}
-         PYTHONWARNINGS=default::DeprecationWarning
+usedevelop = true
+setenv =
+  VIRTUAL_ENV={envdir}
   OS_STDOUT_CAPTURE=1
   OS_STDERR_CAPTURE=1
   OS_TEST_TIMEOUT=60
   OS_TEST_PATH=./cinder/tests/unit
-usedevelop = True
-install_command=python -m pip install -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
-
-deps = -r{toxinidir}/test-requirements.txt
+   PYTHONDONTWRITEBYTECODE=1
+# TODO(stephenfin): Remove once we bump our upper-constraint to SQLAlchemy 2.0
+   SQLALCHEMY_WARN_20=1
+install_command =
+  python -m pip install -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
+deps =
+  -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/requirements.txt
 
 # By default stestr will set concurrency