def METHOD_NAME(self):
    dbus_object = DummyDBusObject()
    self.device_collection.add(DEVICE1_ID, DEVICE1_SERIAL, dbus_object)
    device_obj_by_id = self.device_collection[DEVICE1_ID]
    device_obj_by_serial = self.device_collection[DEVICE1_SERIAL]
    self.assertIs(device_obj_by_id, device_obj_by_serial)