Add min_client_version decorator for CLI tests

This adds the min_client_version decorator to be used in the CLI tests.
The decorator is used skip CLI tests where the command being tested
isn't available in the version of the client we're testing against.

The cmd method is pulled out of the ClientTestBase class so it can be
used by the decorator and is renamed so it does not conflict with the
cmd argument passed to it.

To start using the decorator and show how it works, two known CLI tests
are decorated for minimum version checks on their clients.

Part of blueprint minversion-check-for-cli-tests

Change-Id: I8a0ee390048870d450772fa064d0dc2daa2b7036

test_cli.py

@@ -0,0 +1,59 @@
+# Copyright 2014 IBM Corp.
+#
+#    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
+import testtools
+
+from tempest import cli
+from tempest import exceptions
+from tempest.tests import base
+
+
+class TestMinClientVersion(base.TestCase):
+    """Tests for the min_client_version decorator.
+    """
+
+    def _test_min_version(self, required, installed, expect_skip):
+
+        @cli.min_client_version(client='nova', version=required)
+        def fake(self, expect_skip):
+            if expect_skip:
+                # If we got here, the decorator didn't raise a skipException as
+                # expected so we need to fail.
+                self.fail('Should not have gotten past the decorator.')
+
+        with mock.patch.object(cli, 'execute',
+                               return_value=installed) as mock_cmd:
+            if expect_skip:
+                self.assertRaises(testtools.TestCase.skipException, fake,
+                                  self, expect_skip)
+            else:
+                fake(self, expect_skip)
+            mock_cmd.assert_called_once_with('nova', '', params='--version',
+                                             merge_stderr=True)
+
+    def test_min_client_version(self):
+        # required, installed, expect_skip
+        cases = (('2.17.0', '2.17.0', False),
+                 ('2.17.0', '2.18.0', False),
+                 ('2.18.0', '2.17.0', True))
+
+        for case in cases:
+            self._test_min_version(*case)
+
+    @mock.patch.object(cli, 'execute', return_value=' ')
+    def test_check_client_version_empty_output(self, mock_execute):
+        # Tests that an exception is raised if the command output is empty.
+        self.assertRaises(exceptions.TempestException,
+                          cli.check_client_version, 'nova', '2.18.0')