Add WarningsFixture to only emit DeprecationWarning once in a test run

The nova unit test console output can be flooded with deprecation
warnings from dependent libraries, this change makes it so they are only
logged once.

It's worth noting that Keystone has an alternative implementation where
they filter deprecation warnings and only error out if they are coming
from Keystone code. See commit 9ae6ffe8a.

Partial-Bug: #1407736

Co-authored-by: Sean Dague <sean@dague.net>

Change-Id: Id8d8866baaf64721fda2b6b2e8358db18920c8ba

nova/test.py

@@ -198,6 +198,7 @@ class TestCase(testtools.TestCase):
         self.useFixture(nova_fixtures.OutputStreamCapture())
 
         self.useFixture(nova_fixtures.StandardLogging())
+        self.useFixture(nova_fixtures.WarningsFixture())
 
         # NOTE(sdague): because of the way we were using the lock
         # wrapper we eneded up with a lot of tests that started

nova/tests/fixtures.py

@@ -21,6 +21,7 @@ import gettext
 import logging
 import os
 import uuid
+import warnings
 
 import fixtures
 from oslo.config import cfg
@@ -235,3 +236,15 @@ class RPCFixture(fixtures.Fixture):
         self.messaging_conf.transport_driver = 'fake'
         self.useFixture(self.messaging_conf)
         rpc.init(CONF)
+
+
+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)
+        self.addCleanup(warnings.resetwarnings)