chromium/third_party/blink/web_tests/fast/workers/worker-multi-startup.html

<head>
<p>Test that multipe workers can be spawned simultaneously.
Should print "DONE" when done.</p>
<div id=result></div>
<script>
if (window.testRunner) {
    testRunner.dumpAsText();
    testRunner.waitUntilDone();
}

function log(message)
{
    document.getElementById("result").innerHTML += message + "<br>";
}

totalWorkers = 20;
replies = 0;

for (var i = 0; i < totalWorkers; i++) {
    var worker = new Worker('resources/worker-init.js');
    worker.onmessage = function(evt) {
        log(evt.data);
        if (++replies < totalWorkers)
            return;
        log("DONE");
        if (window.testRunner)
            testRunner.notifyDone();
    }
}
</script>
</body>