Add unit test to validate non DB base core plugin can be loaded

Thanks to the patch I872fa6e3c3925e521150d79bba864101d9a5f648, if a core
plugin is not based on the Neutron DB model, Neutron Manager does not
fail anymore to initialize DB dependent default service plugins.

Change-Id: I948876a7ea7acb0953f622c399dada2148f57571
Partial-Bug: #1700651

neutron/tests/unit/dummy_plugin.py

@@ -22,6 +22,7 @@ from neutron.api import extensions
 from neutron.api.v2 import base
 from neutron.db import servicetype_db
 from neutron.extensions import servicetype
+from neutron import neutron_plugin_base_v2
 
 
 RESOURCE_NAME = "dummy"
@@ -129,3 +130,54 @@ class DummyServicePlugin(service_base.ServicePluginBase):
                                                             svc_type_id)
         except KeyError:
             raise exceptions.NotFound()
+
+
+class DummyCorePluginWithoutDatastore(
+        neutron_plugin_base_v2.NeutronPluginBaseV2):
+    def create_subnet(self, context, subnet):
+        pass
+
+    def update_subnet(self, context, id, subnet):
+        pass
+
+    def get_subnet(self, context, id, fields=None):
+        pass
+
+    def get_subnets(self, context, filters=None, fields=None,
+                    sorts=None, limit=None, marker=None, page_reverse=False):
+        pass
+
+    def delete_subnet(self, context, id):
+        pass
+
+    def create_network(self, context, network):
+        pass
+
+    def update_network(self, context, id, network):
+        pass
+
+    def get_network(self, context, id, fields=None):
+        pass
+
+    def get_networks(self, context, filters=None, fields=None,
+                     sorts=None, limit=None, marker=None, page_reverse=False):
+        pass
+
+    def delete_network(self, context, id):
+        pass
+
+    def create_port(self, context, port):
+        pass
+
+    def update_port(self, context, id, port):
+        pass
+
+    def get_port(self, context, id, fields=None):
+        pass
+
+    def get_ports(self, context, filters=None, fields=None,
+                  sorts=None, limit=None, marker=None, page_reverse=False):
+        pass
+
+    def delete_port(self, context, id):
+        pass

neutron/tests/unit/test_neutron_plugin_base_v2.py

@@ -0,0 +1,26 @@
+# Copyright (c) 2017 OpenStack Foundation.
+#
+#    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.
+
+from oslo_config import cfg
+
+from neutron import manager
+from neutron.tests import base
+
+
+class NeutronPluginBaseV2TestCase(base.BaseTestCase):
+
+    def test_can_load_core_plugin_without_datastore(self):
+        cfg.CONF.set_override("core_plugin", 'neutron.tests.unit.dummy_plugin.'
+                              'DummyCorePluginWithoutDatastore')
+        manager.init()