Deprecations fixture support calling deprecated function

Sometimes a test is expected to call deprecated function, such as
when testing that deprecated function still works. Now the test can
tell the Deprecations fixture that it's calling deprecated function.

Change-Id: Ic7486b74f681989eb5110dfeaf8dae0e5d7ae50e

keystoneclient/tests/unit/client_fixtures.py

@@ -12,6 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import contextlib
 import os
 import warnings
 
@@ -607,3 +608,14 @@ class Deprecations(fixtures.Fixture):
         warnings.filterwarnings('error', category=DeprecationWarning,
                                 module='^keystoneclient\\.')
         self.addCleanup(warnings.resetwarnings)
+
+    def expect_deprecations(self):
+        """Call this if the test expects to call deprecated function."""
+        warnings.resetwarnings()
+
+    @contextlib.contextmanager
+    def expect_deprecations_here(self):
+        warnings.resetwarnings()
+        yield
+        warnings.filterwarnings('error', category=DeprecationWarning,
+                                module='^keystoneclient\\.')

keystoneclient/tests/unit/utils.py

@@ -42,7 +42,7 @@ class TestCase(testtools.TestCase):
 
     def setUp(self):
         super(TestCase, self).setUp()
-        self.useFixture(client_fixtures.Deprecations())
+        self.deprecations = self.useFixture(client_fixtures.Deprecations())
 
         self.logger = self.useFixture(fixtures.FakeLogger(level=logging.DEBUG))
         self.requests_mock = self.useFixture(fixture.Fixture())