Add _get function to base.Manager

This is useful so that we don't have to use _list in each Manager
subclass for getting a single resource and then fetching first item of
the array and checking for index error. This method wraps it for us.

tuskarclient/common/base.py

@@ -52,6 +52,13 @@ class Manager(object):
         if body:
             return self.resource_class(self, body)
 
+    def _get(self, url, **kwargs):
+        kwargs.setdefault('expect_single', True)
+        try:
+            return self._list(url, **kwargs)[0]
+        except IndexError:
+            return None
+
     def _list(self, url, response_key=None, obj_class=None, body=None,
               expect_single=False):
         resp, body = self.api.json_request('GET', url)

tuskarclient/tests/common/test_base.py

@@ -0,0 +1,44 @@
+#    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 mock
+
+from tuskarclient.tests import utils as tutils
+from tuskarclient.common import base
+
+
+class ManagerTest(tutils.TestCase):
+
+    def setUp(self):
+        super(ManagerTest, self).setUp()
+        self.api = mock.Mock()
+        self.m = base.Manager(self.api)
+
+    def test_get(self):
+        self.m._list = mock.Mock(return_value=['fake_resource'])
+        got = self.m._get('url', response_key='response_key',
+                          obj_class='obj_class', body='body')
+
+        self.assertEqual('fake_resource', got)
+        self.m._list.assert_called_with('url', response_key='response_key',
+                                        obj_class='obj_class',
+                                        body='body', expect_single=True)
+
+    def test_get_nonexistent(self):
+        self.m._list = mock.Mock(return_value=[])
+        got = self.m._get('url', response_key='response_key',
+                          obj_class='obj_class', body='body')
+
+        self.assertEqual(None, got)
+        self.m._list.assert_called_with('url', response_key='response_key',
+                                        obj_class='obj_class',
+                                        body='body', expect_single=True)