LayoutTests/media/video-append-source.html

<video controls></video>
<script src=video-test.js></script>
<script>
test("video.currentSrc==''");
var source = document.createElement("source");
source.setAttribute("src", "content/test.mp4");
video.appendChild(source);
test("video.currentSrc==''");
waitForEventTestAndEnd("load", "relativeURL(video.currentSrc)=='content/test.mp4'");
</script>