LayoutTests/svg/animations/begin-event-script.svg

<svg onload="loaded()" xmlns="http://www.w3.org/2000/svg">
<rect id="rect" x="0" y="0" width="50" height="50" fill="red">
    <animate id="anim" attributeName="visibility" to="visible" begin="1s" end="2s" />
</rect>
<script>
    if (window.testRunner)
        testRunner.waitUntilDone();

    function loaded() {
        document.getElementById("anim").addEventListener("beginEvent", function(event) {
            document.getElementById("rect").setAttribute("fill", "green");
            testRunner.notifyDone();
        });

        document.documentElement.setCurrentTime(1);
    }

</script>
</svg>