[CORD-3008] Before removing OLT check that no subscribers are using it

Change-Id: I7f3d0f9d552a74a05c3f447cbb35b75f29595c87
diff --git a/xos/synchronizer/models/test_oltdevice_model.py b/xos/synchronizer/models/test_oltdevice_model.py
new file mode 100644
index 0000000..34bf200
--- /dev/null
+++ b/xos/synchronizer/models/test_oltdevice_model.py
@@ -0,0 +1,77 @@
+# Copyright 2017-present Open Networking 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.
+
+import unittest
+from mock import patch, Mock, MagicMock
+
+# mocking XOS exception, as they're based in Django
+class Exceptions:
+    XOSValidationError = Exception
+
+class XOS:
+    exceptions = Exceptions
+
+class TestOLTDeviceModel(unittest.TestCase):
+    def setUp(self):
+        self.xos = XOS
+
+        self.models_decl = Mock()
+        self.models_decl.OLTDevice_decl = MagicMock
+        self.models_decl.OLTDevice_decl.delete = Mock()
+
+        modules = {
+            'xos.exceptions': self.xos.exceptions,
+            'models_decl': self.models_decl,
+        }
+
+        self.module_patcher = patch.dict('sys.modules', modules)
+        self.module_patcher.start()
+
+        from models import OLTDevice
+
+        print OLTDevice
+
+        self.olt_device = OLTDevice()
+        self.olt_device.id = None # this is a new model
+        self.olt_device.is_new = True
+        self.olt_device.device_id = 1234
+
+
+    def test_delete(self):
+        self.olt_device.delete()
+        self.models_decl.OLTDevice_decl.delete.assert_called()
+
+    def test_prevent_delete(self):
+
+        onu1 = Mock()
+        onu1.id = 1
+
+        pon1 = Mock()
+        pon1.onu_devices.all.return_value = [onu1]
+
+        self.olt_device.pon_ports.all.return_value = [pon1]
+
+        volt_si_1 = Mock()
+        volt_si_1.onu_device_id = onu1.id
+
+        with patch.object(self.olt_device, "get_volt_si")as volt_si_get:
+            volt_si_get.return_value = [volt_si_1]
+            with self.assertRaises(Exception) as e:
+                self.olt_device.delete()
+
+            self.assertEqual(e.exception.message, 'OLT "1234" can\'t be deleted as it has subscribers associated with its ONUs')
+            self.models_decl.OLTDevice_decl.delete.assert_not_called()
+
+if __name__ == '__main__':
+    unittest.main()