default to no network-device-mtu

unit_tests/test_neutron_api_hooks.py

@@ -273,6 +273,21 @@ class NeutronAPIHooksTests(CharmTestCase):
         self.assertTrue(self.CONFIGS.write.called_with(NEUTRON_CONF))
 
     def test_neutron_plugin_api_relation_joined_nol2(self):
+        _relation_data = {
+            'neutron-security-groups': False,
+            'l2-population': False,
+            'overlay-network-type': 'vxlan',
+        }
+        self.get_l2population.return_value = False
+        self.get_overlay_network_type.return_value = 'vxlan'
+        self._call_hook('neutron-plugin-api-relation-joined')
+        self.relation_set.assert_called_with(
+            relation_id=None,
+            **_relation_data
+        )
+
+    def test_neutron_plugin_api_relation_joined_w_mtu(self):
+        self.test_config.set('network-device-mtu', 1500)
         _relation_data = {
             'neutron-security-groups': False,
             'l2-population': False,