diff --git a/manilaclient/common/apiclient/auth.py b/manilaclient/common/apiclient/auth.py
index a2250da..ed640a1 100644
--- a/manilaclient/common/apiclient/auth.py
+++ b/manilaclient/common/apiclient/auth.py
@@ -25,7 +25,7 @@ import six
 from stevedore import extension
 
 from manilaclient.common.apiclient import exceptions
-
+from manilaclient.common import constants
 
 _discovered_plugins = {}
 
@@ -41,8 +41,7 @@ def discover_auth_systems():
     def add_plugin(ext):
         _discovered_plugins[ext.name] = ext.plugin
 
-    ep_namespace = "manilaclient.common.apiclient.auth"
-    mgr = extension.ExtensionManager(ep_namespace)
+    mgr = extension.ExtensionManager(constants.EXTENSION_PLUGIN_NAMESPACE)
     mgr.map(add_plugin)
 
 
diff --git a/manilaclient/common/constants.py b/manilaclient/common/constants.py
index 4e0814f..5249f83 100644
--- a/manilaclient/common/constants.py
+++ b/manilaclient/common/constants.py
@@ -79,3 +79,5 @@ V1_SERVICE_TYPE = 'share'
 V2_SERVICE_TYPE = 'sharev2'
 
 SERVICE_TYPES = {'1': V1_SERVICE_TYPE, '2': V2_SERVICE_TYPE}
+
+EXTENSION_PLUGIN_NAMESPACE = 'manilaclient.common.apiclient.auth'
diff --git a/manilaclient/tests/unit/common/apiclient/__init__.py b/manilaclient/tests/unit/common/apiclient/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/manilaclient/tests/unit/common/apiclient/test_auth.py b/manilaclient/tests/unit/common/apiclient/test_auth.py
new file mode 100644
index 0000000..035f344
--- /dev/null
+++ b/manilaclient/tests/unit/common/apiclient/test_auth.py
@@ -0,0 +1,48 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import ddt
+import mock
+
+from manilaclient.common.apiclient import auth
+from manilaclient.common import constants
+from manilaclient.tests.unit import utils
+
+
+@ddt.ddt
+class DiscoverAuthSystems(utils.TestCase):
+
+    @ddt.unpack
+    @ddt.data(
+        {'plugins': {'a': 42, 'b': 'bar'}, 'discovered': {}},
+        {'plugins': {'a': 42, 'b': 'bar'}, 'discovered': {'b': 'overwrite'}},
+        {'plugins': {'a': 42, 'b': 'bar'}, 'discovered': {'c': 'reset'}}
+    )
+    @mock.patch.dict('stevedore.extension.ExtensionManager.ENTRY_POINT_CACHE',
+                     clear=True)
+    def test_plugins(self, plugins, discovered):
+        mock_plugins = []
+        for name, return_value in plugins.items():
+            plugin = mock.Mock()
+            plugin.resolve = mock.Mock(return_value=return_value)
+            plugin.name = name
+            mock_plugins.append(plugin)
+        with mock.patch.dict(
+                'manilaclient.common.apiclient.auth._discovered_plugins',
+                discovered, clear=True):
+            with mock.patch('pkg_resources.iter_entry_points') as ep_mock:
+                ep_mock.return_value = mock_plugins
+                auth.discover_auth_systems()
+                ep_mock.assert_called_with(
+                    constants.EXTENSION_PLUGIN_NAMESPACE
+                )
+                self.assertEqual(plugins, auth._discovered_plugins)