Add fixture to only emit DeprecationWarning once

We have a ton of DeprecationWarning messages in our unit test runs.
Most of these are out of our control from third party libs. This
adds a WarningsFixture to limit warning output to once per test
run, getting rid of >700 warnings in our logs.

Borrowed heavily from Id8d8866baaf64721fda2b6b2e8358db18920c8ba and
I5eaf953b6a2b0a3efe215f776aa048433b192e90 in Nova.

Change-Id: I2250d4bad1b1f7d1f83c175a5e2b124f02ec9212

cinder/test.py

@@ -210,6 +210,10 @@ def setUp(self):
                                  sql_connection=CONF.database.connection)
         self.useFixture(_DB_CACHE)
 
+        # NOTE(blk-u): WarningsFixture must be after the Database fixture
+        # because sqlalchemy-migrate messes with the warnings filters.
+        self.useFixture(cinder_fixtures.WarningsFixture())
+
         # NOTE(danms): Make sure to reset us back to non-remote objects
         # for each test to avoid interactions. Also, backup the object
         # registry.

cinder/tests/fixtures.py

@@ -18,6 +18,7 @@
 
 import logging as std_logging
 import os
+import warnings
 
 import fixtures
 
@@ -110,3 +111,23 @@ def fake_logging_setup(*args):
 
         self.useFixture(
             fixtures.MonkeyPatch('oslo_log.log.setup', fake_logging_setup))
+
+
+class WarningsFixture(fixtures.Fixture):
+    """Filters out warnings during test runs."""
+
+    def setUp(self):
+        super(WarningsFixture, self).setUp()
+        # NOTE(sdague): Make deprecation warnings only happen once. Otherwise
+        # this gets kind of crazy given the way that upstream python libs use
+        # this.
+        warnings.simplefilter('once', DeprecationWarning)
+
+        # NOTE(sdague): this remains an unresolved item around the way
+        # forward on is_admin, the deprecation is definitely really premature.
+        warnings.filterwarnings(
+            'ignore',
+            message='Policy enforcement is depending on the value of is_admin.'
+                    ' This key is deprecated. Please update your policy '
+                    'file to use the standard policy values.')
+        self.addCleanup(warnings.resetwarnings)