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chromium/third_party/blink/web_tests/media/video-source-none-supported.html 

<!DOCTYPE html>
<title>Test that no usable "source" element leaves the media element with networkState == NETWORK_NO_SOURCE.</title>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>
<video>
    <source src="test.mp4" type="audio/x-chicken-face"></source>
    <source src="test.ogv" type="video/x-higglety-pigglety"></source>
    <source src="doesnotexist.mp4"></source>
</video>
<script>
async_test(function(t) {
    var errorCount = 0;
    var video = document.querySelector("video");

    var sourceList = document.querySelectorAll("source");
    for (var source of sourceList) {
        source.onerror = t.step_func(function(event) {
            errorCount++;
            if (errorCount < 3) {
                // Because the error event is fired asynchronously the network state
                // can be either NETWORK_LOADING or NETWORK_NO_SOURCE, depending on
                // whether or not any pending "source" element is available.
                assert_greater_than(video.networkState, HTMLMediaElement.NETWORK_IDLE);
            } else {
                assert_equals(video.networkState, HTMLMediaElement.NETWORK_NO_SOURCE);
                t.done();
            }
        });
    }
});
</script>