diff --git a/neutron/tests/tools.py b/neutron/tests/tools.py
index df54634a2ee..82b2d493032 100644
--- a/neutron/tests/tools.py
+++ b/neutron/tests/tools.py
@@ -34,6 +34,17 @@ from neutron.common import constants as n_const
 from neutron.services.logapi.common import constants as log_const
 
 
+# NOTE(yamahata): from neutron-lib 1.9.1, callback priority was added and
+# priority_group module was added for constants of priority.
+# test the existence of the module of priority_group to check if
+# callback priority is supported or not.
+CALLBACK_PRIORITY_SUPPORTED = True
+try:
+    from neutron_lib.callbacks import priority_group  # noqa
+except ImportError as e:
+    CALLBACK_PRIORITY_SUPPORTED = False
+
+
 class WarningsFixture(fixtures.Fixture):
     """Filters out warnings during test runs."""
 
@@ -135,6 +146,16 @@ def verify_mock_calls(mocked_call, expected_calls_and_values,
     mocked_call.assert_has_calls(expected_calls, any_order=any_order)
 
 
+def get_subscribe_args(*args):
+    # NOTE(yamahata): from neutron-lib 1.9.1, callback priority was added.
+    # old signature: (callback, resource, event)
+    # new signature: (callback, resource, event, priority=PRIORITY_DEFAULT)
+    if len(args) == 3 and CALLBACK_PRIORITY_SUPPORTED:
+        args = list(args)  # don't modify original list
+        args.append(priority_group.PRIORITY_DEFAULT)
+    return args
+
+
 def fail(msg=None):
     """Fail immediately, with the given message.
 
diff --git a/neutron/tests/unit/plugins/ml2/drivers/agent/test_capabilities.py b/neutron/tests/unit/plugins/ml2/drivers/agent/test_capabilities.py
index 79f56de8124..90b932af441 100644
--- a/neutron/tests/unit/plugins/ml2/drivers/agent/test_capabilities.py
+++ b/neutron/tests/unit/plugins/ml2/drivers/agent/test_capabilities.py
@@ -17,6 +17,7 @@ from neutron_lib import fixture
 
 from neutron.plugins.ml2.drivers.agent import capabilities
 from neutron.tests import base
+from neutron.tests import tools
 
 
 class CapabilitiesTest(base.BaseTestCase):
@@ -40,6 +41,6 @@ class CapabilitiesTest(base.BaseTestCase):
         mock_callback = mock.Mock()
         mock_agent_type = mock.Mock()
         capabilities.register(mock_callback, mock_agent_type)
-        self._mgr.subscribe.assert_called_with(mock_callback,
-                                               mock_agent_type,
-                                               events.AFTER_INIT)
+        args = tools.get_subscribe_args(
+            mock_callback, mock_agent_type, events.AFTER_INIT)
+        self._mgr.subscribe.assert_called_with(*args)
diff --git a/neutron/tests/unit/plugins/ml2/drivers/openvswitch/agent/test_ovs_capabilities.py b/neutron/tests/unit/plugins/ml2/drivers/openvswitch/agent/test_ovs_capabilities.py
index 6b20c86f4e2..75947922311 100644
--- a/neutron/tests/unit/plugins/ml2/drivers/openvswitch/agent/test_ovs_capabilities.py
+++ b/neutron/tests/unit/plugins/ml2/drivers/openvswitch/agent/test_ovs_capabilities.py
@@ -19,6 +19,7 @@ from neutron_lib import fixture
 from neutron.plugins.ml2.drivers.openvswitch.agent import ovs_capabilities
 from neutron.services.trunk.drivers.openvswitch.agent import driver
 from neutron.tests import base
+from neutron.tests import tools
 from neutron_lib import constants
 
 
@@ -32,6 +33,6 @@ class CapabilitiesTest(base.BaseTestCase):
 
     def test_register(self):
         ovs_capabilities.register()
-        self._mgr.subscribe.assert_called_with(driver.init_handler,
-                                            constants.AGENT_TYPE_OVS,
-                                            events.AFTER_INIT)
+        args = tools.get_subscribe_args(
+            driver.init_handler, constants.AGENT_TYPE_OVS, events.AFTER_INIT)
+        self._mgr.subscribe.assert_called_with(*args)
diff --git a/neutron/tests/unit/services/trunk/rpc/test_backend.py b/neutron/tests/unit/services/trunk/rpc/test_backend.py
index 00ec02ed847..ea1ba32c45c 100644
--- a/neutron/tests/unit/services/trunk/rpc/test_backend.py
+++ b/neutron/tests/unit/services/trunk/rpc/test_backend.py
@@ -20,6 +20,7 @@ from neutron.services.trunk import callbacks
 from neutron.services.trunk import constants as trunk_consts
 from neutron.services.trunk.rpc import backend
 from neutron.tests import base
+from neutron.tests import tools
 
 
 class ServerSideRpcBackendTest(base.BaseTestCase):
@@ -35,18 +36,26 @@ class ServerSideRpcBackendTest(base.BaseTestCase):
     def test___init__(self,):
         test_obj = backend.ServerSideRpcBackend()
 
-        calls = [mock.call(test_obj.process_event,
-                           trunk_consts.TRUNK,
-                           events.AFTER_CREATE),
-                 mock.call(test_obj.process_event,
-                           trunk_consts.TRUNK,
-                           events.AFTER_DELETE),
-                 mock.call(test_obj.process_event,
-                           trunk_consts.SUBPORTS,
-                           events.AFTER_CREATE),
-                 mock.call(test_obj.process_event,
-                           trunk_consts.SUBPORTS,
-                           events.AFTER_DELETE)
+        calls = [mock.call(
+                    *tools.get_subscribe_args(
+                        test_obj.process_event,
+                        trunk_consts.TRUNK,
+                        events.AFTER_CREATE)),
+                 mock.call(
+                    *tools.get_subscribe_args(
+                        test_obj.process_event,
+                        trunk_consts.TRUNK,
+                        events.AFTER_DELETE)),
+                 mock.call(
+                    *tools.get_subscribe_args(
+                        test_obj.process_event,
+                        trunk_consts.SUBPORTS,
+                        events.AFTER_CREATE)),
+                 mock.call(
+                    *tools.get_subscribe_args(
+                        test_obj.process_event,
+                        trunk_consts.SUBPORTS,
+                        events.AFTER_DELETE))
                  ]
         self._mgr.subscribe.assert_has_calls(calls, any_order=True)