flex – 如何判断实例是否在ActionScript 3.0中实现了接口

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark" xmlns:mx="library://ns.adobe.com/flex/halo" minWidth="1024" minHeight="768" creationComplete="application1_creationCompleteHandler(event)">
    <fx:Script>
        <![CDATA[
            import mx.events.FlexEvent;
            public var test:TestInterface = new TestInterface() //implements ITestInterface


            protected function application1_creationCompleteHandler(event:FlexEvent):void
            {
                trace(test is ITestInterface); //true
            }

        ]]>
    </fx:Script>
</s:Application>