Add a DatabasePoisonFixture

This is the beginning of a poison fixture for tests that don't use
the database. If they do, we interrupt them deep in oslo_db, log a
warning, and return a MagicMock. This keeps them from breaking
global database state, but doesn't actually poison them. This should
be followed-up with a patch to raise an exception, and fix the rest
of the tests that depend on the broken behavior.

Since some tests claim to not be DB test, but use the fixture
themselves anyway, this adds a USES_DB_SELF flag to help gate
the application of the poison.

Change-Id: If071a12a33aad86e918a9f441a246a930e921c8d

nova/test.py

@@ -170,6 +170,7 @@ class TestCase(testtools.TestCase):
     `NoDBTestCase` first.
     """
     USES_DB = True
+    USES_DB_SELF = False
     REQUIRES_LOCKING = False
 
     TIMEOUT_SCALING_FACTOR = 1
@@ -213,6 +214,8 @@ class TestCase(testtools.TestCase):
         if self.USES_DB:
             self.useFixture(nova_fixtures.Database())
             self.useFixture(nova_fixtures.Database(database='api'))
+        elif not self.USES_DB_SELF:
+            self.useFixture(nova_fixtures.DatabasePoisonFixture())
 
         # NOTE(blk-u): WarningsFixture must be after the Database fixture
         # because sqlalchemy-migrate messes with the warnings filters.

nova/tests/fixtures.py

@@ -22,6 +22,7 @@ import os
 import warnings
 
 import fixtures
+import mock
 from oslo_config import cfg
 from oslo_db.sqlalchemy import enginefacade
 from oslo_messaging import conffixture as messaging_conffixture
@@ -196,6 +197,22 @@ class Timeout(fixtures.Fixture):
             self.useFixture(fixtures.Timeout(self.test_timeout, gentle=True))
 
 
+class DatabasePoisonFixture(fixtures.Fixture):
+    def setUp(self):
+        super(DatabasePoisonFixture, self).setUp()
+        self.useFixture(fixtures.MonkeyPatch(
+            'oslo_db.sqlalchemy.enginefacade._TransactionFactory.'
+            '_create_session',
+            self._poison_configure))
+
+    def _poison_configure(self, *a, **k):
+        warnings.warn('This test uses methods that set internal oslo_db '
+                      'state, but it does not claim to use the database. '
+                      'This will conflict with the setup of tests that '
+                      'do use the database and cause failures later.')
+        return mock.MagicMock()
+
+
 class Database(fixtures.Fixture):
     def __init__(self, database='main', connection=None):
         """Create a database fixture.

nova/tests/functional/db/test_build_request.py

@@ -24,6 +24,8 @@ from nova.tests.unit import fake_request_spec
 
 
 class BuildRequestTestCase(test.NoDBTestCase):
+    USES_DB_SELF = True
+
     def setUp(self):
         super(BuildRequestTestCase, self).setUp()
         # NOTE: This means that we're using a database for this test suite

nova/tests/functional/db/test_cell_mapping.py

@@ -20,6 +20,8 @@ from nova.tests import fixtures
 
 
 class CellMappingTestCase(test.NoDBTestCase):
+    USES_DB_SELF = True
+
     def setUp(self):
         super(CellMappingTestCase, self).setUp()
         self.useFixture(fixtures.Database(database='api'))

nova/tests/functional/db/test_connection_switch.py

@@ -22,6 +22,7 @@ from nova.tests import fixtures
 
 
 class ConnectionSwitchTestCase(test.NoDBTestCase):
+    USES_DB_SELF = True
     test_filename = 'foo.db'
 
     def setUp(self):

nova/tests/functional/db/test_host_mapping.py

@@ -57,6 +57,8 @@ def create_mapping_obj(context, **kwargs):
 
 
 class HostMappingTestCase(test.NoDBTestCase):
+    USES_DB_SELF = True
+
     def setUp(self):
         super(HostMappingTestCase, self).setUp()
         self.useFixture(fixtures.Database(database='api'))

nova/tests/functional/db/test_instance_mapping.py

@@ -34,6 +34,8 @@ def create_mapping(**kwargs):
 
 
 class InstanceMappingTestCase(test.NoDBTestCase):
+    USES_DB_SELF = True
+
     def setUp(self):
         super(InstanceMappingTestCase, self).setUp()
         self.useFixture(fixtures.Database(database='api'))

nova/tests/functional/db/test_request_spec.py

@@ -20,6 +20,8 @@ from nova.tests.unit import fake_request_spec
 
 
 class RequestSpecTestCase(test.NoDBTestCase):
+    USES_DB_SELF = True
+
     def setUp(self):
         super(RequestSpecTestCase, self).setUp()
         self.useFixture(fixtures.Database(database='api'))

nova/tests/functional/db/test_resource_provider.py

@@ -31,6 +31,8 @@ DISK_INVENTORY = dict(
 class ResourceProviderTestCase(test.NoDBTestCase):
     """Test resource-provider objects' lifecycles."""
 
+    USES_DB_SELF = True
+
     def setUp(self):
         super(ResourceProviderTestCase, self).setUp()
         self.useFixture(fixtures.Database())