chromium/third_party/blink/web_tests/media/audio-constructor-preload.html

<!DOCTYPE html>
<title>Test that Audio() sets "preload" attribute.</title>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>
<script>
async_test(function(t) {
    var audio = new Audio();

    // Test initial attribute value.
    assert_equals(audio.getAttribute("preload"), "auto");
    assert_equals(audio.preload, "auto");

    audio.oncanplaythrough = t.step_func_done(function() {
        assert_equals(audio.getAttribute("preload"), "auto");
        assert_equals(audio.preload, "auto");
    });

    audio.src = "content/test.oga";
    audio.load();
});
</script>