ovs: Fix error in patch_ports_on_bridge (juju#509)

The unit test for patch_ports_on_bridge was not quite good enough
and hid the fact that the function now always raises ValueError.

This patch fixes both.

charmhelpers/contrib/network/ovs/__init__.py

@@ -649,6 +649,11 @@ def patch_ports_on_bridge(bridge):
                         interface['options']['peer'])),
                     interface['options']['peer'])
                 yield(Patch(this_end, other_end))
+            # We expect one result and it is ok if it turns out to be a port
+            # for a different bridge. However we need a break here to satisfy
+            # the for/else check which is in place to detect interface refering
+            # to non-existent port.
+            break
         else:
             raise ValueError('Port for interface named "{}" does unexpectedly '
                              'not exist.'.format(interface['name']))

tests/contrib/network/ovs/test_ovs.py

@@ -219,8 +219,15 @@ def test_bridge_for_port(self):
     def test_patch_ports_on_bridge(self):
         self.patch_object(ovs.ch_ovsdb, 'SimpleOVSDB')
         self.patch_object(ovs, 'bridge_for_port')
+        self.patch_object(ovs, 'uuid_for_port')
         ovsdb = mock.MagicMock()
         ovsdb.interface.find.return_value = [
+            {
+                'name': 'fake-interface-with-port-for-other-bridge',
+                'options': {
+                    'peer': 'fake-peer'
+                },
+            },
             {
                 'name': 'fake-interface',
                 'options': {
@@ -229,14 +236,18 @@ def test_patch_ports_on_bridge(self):
             },
         ]
         port_uuid = uuid.UUID('0d43905b-f80e-4eaa-9feb-a9017da8c6bc')
-        ovsdb.port.find.return_value = [
-            {
+        ovsdb.port.find.side_effect = [
+            [{
+                '_uuid': port_uuid,
+                'name': 'port-on-other-bridge',
+            }],
+            [{
                 '_uuid': port_uuid,
                 'name': 'fake-port',
-            },
+            }],
         ]
         self.SimpleOVSDB.return_value = ovsdb
-        self.bridge_for_port.side_effect = ['fake-bridge', 'fake-peer-bridge']
+        self.bridge_for_port.side_effect = ['some-other-bridge', 'fake-bridge', 'fake-peer-bridge']
         for patch in ovs.patch_ports_on_bridge('fake-bridge'):
             self.assertEquals(
                 patch,
@@ -251,6 +262,7 @@ def test_patch_ports_on_bridge(self):
             break
         else:
             assert 0, 'Expected generator to provide output'
+        ovsdb.port.find.side_effect = None
         ovsdb.port.find.return_value = []
         with self.assertRaises(ValueError):
             for patch in ovs.patch_ports_on_bridge('fake-bridge'):