diff --git a/ceilometer/service.py b/ceilometer/service.py
index e6e68ed2..aac72424 100644
--- a/ceilometer/service.py
+++ b/ceilometer/service.py
@@ -112,7 +112,7 @@ cfg.CONF.register_opt(COLL_OPT, 'collector')
 LOG = log.getLogger(__name__)
 
 
-def prepare_service(argv=None):
+def prepare_service(argv=None, config_files=None):
     oslo_i18n.enable_lazy()
     log.register_options(cfg.CONF)
     log_levels = (cfg.CONF.default_log_levels +
@@ -121,7 +121,8 @@ def prepare_service(argv=None):
     if argv is None:
         argv = sys.argv
     cfg.CONF(argv[1:], project='ceilometer', validate_default_values=True,
-             version=version.version_info.version_string())
+             version=version.version_info.version_string(),
+             default_config_files=config_files)
     log.setup(cfg.CONF, 'ceilometer')
     # NOTE(liusheng): guru cannot run with service under apache daemon, so when
     # ceilometer-api running with mod_wsgi, the argv is [], we don't start
diff --git a/ceilometer/tests/functional/gabbi/fixtures.py b/ceilometer/tests/functional/gabbi/fixtures.py
index 437b2e38..76ddd47e 100644
--- a/ceilometer/tests/functional/gabbi/fixtures.py
+++ b/ceilometer/tests/functional/gabbi/fixtures.py
@@ -56,7 +56,7 @@ class ConfigFixture(fixture.GabbiFixture):
         if db_url is None:
             raise case.SkipTest('No database connection configured')
 
-        service.prepare_service([])
+        service.prepare_service(argv=[], config_files=[])
         conf = fixture_config.Config().conf
         self.conf = conf
         opts.set_defaults(self.conf)
diff --git a/ceilometer/tests/functional/test_notification.py b/ceilometer/tests/functional/test_notification.py
index e55b6f5b..e053540c 100644
--- a/ceilometer/tests/functional/test_notification.py
+++ b/ceilometer/tests/functional/test_notification.py
@@ -199,7 +199,8 @@ class BaseRealNotification(tests_base.BaseTestCase):
     def setUp(self):
         super(BaseRealNotification, self).setUp()
         self.CONF = self.useFixture(fixture_config.Config()).conf
-        service.prepare_service([])
+        # Dummy config file to avoid looking for system config
+        service.prepare_service(argv=[], config_files=[])
         self.setup_messaging(self.CONF, 'nova')
 
         pipeline_cfg_file = self.setup_pipeline(['instance', 'memory'])
@@ -452,7 +453,7 @@ class TestRealNotificationMultipleAgents(tests_base.BaseTestCase):
     def setUp(self):
         super(TestRealNotificationMultipleAgents, self).setUp()
         self.CONF = self.useFixture(fixture_config.Config()).conf
-        service.prepare_service([])
+        service.prepare_service(argv=[], config_files=[])
         self.setup_messaging(self.CONF, 'nova')
 
         pipeline_cfg_file = self.setup_pipeline(['instance', 'memory'])
diff --git a/ceilometer/tests/unit/dispatcher/test_gnocchi.py b/ceilometer/tests/unit/dispatcher/test_gnocchi.py
index 1c48c222..7c10f168 100644
--- a/ceilometer/tests/unit/dispatcher/test_gnocchi.py
+++ b/ceilometer/tests/unit/dispatcher/test_gnocchi.py
@@ -53,7 +53,7 @@ class DispatcherTest(base.BaseTestCase):
     def setUp(self):
         super(DispatcherTest, self).setUp()
         self.conf = self.useFixture(config_fixture.Config())
-        ceilometer_service.prepare_service([])
+        ceilometer_service.prepare_service(argv=[], config_files=[])
         self.conf.config(
             resources_definition_file=self.path_get(
                 'etc/ceilometer/gnocchi_resources.yaml'),
@@ -330,7 +330,7 @@ class DispatcherWorkflowTest(base.BaseTestCase,
             return_value=ks_client))
         self.ks_client = ks_client
 
-        ceilometer_service.prepare_service([])
+        ceilometer_service.prepare_service(argv=[], config_files=[])
         self.conf.config(
             resources_definition_file=self.path_get(
                 'etc/ceilometer/gnocchi_resources.yaml'),
diff --git a/ceilometer/tests/unit/meter/test_notifications.py b/ceilometer/tests/unit/meter/test_notifications.py
index ba7f0eaf..30446b2a 100644
--- a/ceilometer/tests/unit/meter/test_notifications.py
+++ b/ceilometer/tests/unit/meter/test_notifications.py
@@ -193,7 +193,7 @@ class TestMeterProcessing(test.BaseTestCase):
     def setUp(self):
         super(TestMeterProcessing, self).setUp()
         self.CONF = self.useFixture(fixture_config.Config()).conf
-        ceilometer_service.prepare_service([])
+        ceilometer_service.prepare_service(argv=[], config_files=[])
         self.handler = notifications.ProcessMeterNotifications(mock.Mock())
 
     def test_fallback_meter_path(self):
diff --git a/ceilometer/tests/unit/network/statistics/opencontrail/test_client.py b/ceilometer/tests/unit/network/statistics/opencontrail/test_client.py
index f0eec1f5..fdee69c9 100644
--- a/ceilometer/tests/unit/network/statistics/opencontrail/test_client.py
+++ b/ceilometer/tests/unit/network/statistics/opencontrail/test_client.py
@@ -25,7 +25,7 @@ class TestOpencontrailClient(base.BaseTestCase):
     def setUp(self):
         super(TestOpencontrailClient, self).setUp()
         self.conf = self.useFixture(config_fixture.Config())
-        ceilometer_service.prepare_service([])
+        ceilometer_service.prepare_service(argv=[], config_files=[])
         self.client = client.Client('http://127.0.0.1:8081', {'arg1': 'aaa'})
 
         self.get_resp = mock.MagicMock()
diff --git a/ceilometer/tests/unit/network/statistics/opendaylight/test_client.py b/ceilometer/tests/unit/network/statistics/opendaylight/test_client.py
index 5fa1f26d..7b2250ee 100644
--- a/ceilometer/tests/unit/network/statistics/opendaylight/test_client.py
+++ b/ceilometer/tests/unit/network/statistics/opendaylight/test_client.py
@@ -32,7 +32,7 @@ class TestClientHTTPBasicAuth(base.BaseTestCase):
     def setUp(self):
         super(TestClientHTTPBasicAuth, self).setUp()
         self.conf = self.useFixture(config_fixture.Config())
-        ceilometer_service.prepare_service([])
+        ceilometer_service.prepare_service(argv=[], config_files=[])
         self.parsed_url = urlparse.urlparse(
             'http://127.0.0.1:8080/controller/nb/v2?container_name=default&'
             'container_name=egg&auth=%s&user=admin&password=admin_pass&'