container.beforeCollectionChanges(action)

        when:
        container.add("a")

        then:
        1 * action.execute(null)
        0 * _
    }

    def objectIsNotAddedWhenVetoActionThrowsAnException() {
        def action = Mock(Action)
        def failure = new RuntimeException()
        container.beforeCollectionChanges(action)

        when:
        container.add("a")

        then: