c.items.add new Widget()
                c.widgets.add new Widget()
                c.rawWidgets.add new Widget()
            }

            @Mutate
            void addCheckTask(ModelMap<Task> tasks, Container c) {
                tasks.create('check') {
                    assert c.items.size() == 1
                    assert c.widgets.size() == 1
                    assert c.rawWidgets.size() == 1