make the driver.Scheduler as abstract class

method select_destinations is the abstract method, every subclass
of Scheduler should override, so add abstractmethod decorator

Change-Id: Ib9edd7ac9fc024543efb0b878431fa8351c68a45

nova/scheduler/driver.py

@@ -19,11 +19,13 @@
 Scheduler base class that all Schedulers should inherit from
 """
 
+import abc
+
 from oslo_config import cfg
 from oslo_utils import importutils
+import six
 
 from nova import db
-from nova.i18n import _
 from nova import servicegroup
 
 scheduler_driver_opts = [
@@ -36,6 +38,7 @@ CONF = cfg.CONF
 CONF.register_opts(scheduler_driver_opts)
 
 
+@six.add_metaclass(abc.ABCMeta)
 class Scheduler(object):
     """The base class that all Scheduler classes should inherit from."""
 
@@ -56,11 +59,11 @@ class Scheduler(object):
                 for service in services
                 if self.servicegroup_api.service_is_up(service)]
 
+    @abc.abstractmethod
     def select_destinations(self, context, request_spec, filter_properties):
         """Must override select_destinations method.
 
         :return: A list of dicts with 'host', 'nodename' and 'limits' as keys
             that satisfies the request_spec and filter_properties.
         """
-        msg = _("Driver must implement select_destinations")
-        raise NotImplementedError(msg)
+        return []

nova/tests/unit/scheduler/fakes.py

@@ -19,6 +19,7 @@ Fakes For Scheduler tests.
 import six
 
 from nova import objects
+from nova.scheduler import driver
 from nova.scheduler import host_manager
 
 NUMA_TOPOLOGY = objects.NUMATopology(
@@ -96,3 +97,9 @@ class FakeHostState(host_manager.HostState):
             self.instances = {}
         for (key, val) in six.iteritems(attribute_dict):
             setattr(self, key, val)
+
+
+class FakeScheduler(driver.Scheduler):
+
+    def select_destinations(self, context, request_spec, filter_properties):
+        return []

nova/tests/unit/scheduler/test_scheduler.py

@@ -21,20 +21,20 @@ import mock
 
 from nova import context
 from nova import db
-from nova.scheduler import driver
 from nova.scheduler import host_manager
 from nova.scheduler import manager
 from nova import servicegroup
 from nova import test
 from nova.tests.unit import fake_server_actions
+from nova.tests.unit.scheduler import fakes
 
 
 class SchedulerManagerTestCase(test.NoDBTestCase):
     """Test case for scheduler manager."""
 
     manager_cls = manager.SchedulerManager
-    driver_cls = driver.Scheduler
-    driver_cls_name = 'nova.scheduler.driver.Scheduler'
+    driver_cls = fakes.FakeScheduler
+    driver_cls_name = 'nova.tests.unit.scheduler.fakes.FakeScheduler'
 
     @mock.patch.object(host_manager.HostManager, '_init_instance_info')
     @mock.patch.object(host_manager.HostManager, '_init_aggregates')
@@ -109,7 +109,7 @@ class SchedulerTestCase(test.NoDBTestCase):
     """Test case for base scheduler driver class."""
 
     # So we can subclass this test and re-use tests if we need.
-    driver_cls = driver.Scheduler
+    driver_cls = fakes.FakeScheduler
 
     @mock.patch.object(host_manager.HostManager, '_init_instance_info')
     @mock.patch.object(host_manager.HostManager, '_init_aggregates')
@@ -138,19 +138,9 @@ class SchedulerTestCase(test.NoDBTestCase):
         self.assertEqual(result, ['host2'])
 
 
-class SchedulerDriverBaseTestCase(SchedulerTestCase):
-    """Test cases for base scheduler driver class methods
-       that will fail if the driver is changed.
-    """
-
-    def test_unimplemented_select_destinations(self):
-        self.assertRaises(NotImplementedError,
-                self.driver.select_destinations, self.context, {}, {})
-
-
 class SchedulerInstanceGroupData(test.NoDBTestCase):
 
-    driver_cls = driver.Scheduler
+    driver_cls = fakes.FakeScheduler
 
     def setUp(self):
         super(SchedulerInstanceGroupData, self).setUp()