<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-fonts-4/#font-display-timeline">
<script nonce="abc" src="/resources/testharness.js"></script>
<script nonce="abc" src="/resources/testharnessreport.js"></script>
<style>
@font-face {
  font-family: 'TestFace';
  src: url('/fonts/Ahem.ttf?pipe=trickle(d0.5)'),
       url('/fonts/Ahem.ttf?fallback-src');
  font-display: optional;
}

@font-face {
  font-family: 'FallbackFace';
  src: url('/fonts/Ahem.ttf?fallback-face');
}

.test {
  font-family: 'TestFace','FallbackFace';
}
</style>
<div class="test">hello</div>
<script>
function numberOfDownloads(url) {
    assert_true(!!window.PerformanceResourceTiming, "ResourceTiming not supported");
    var absoluteURL = new URL(url, location.href).href;
    return performance.getEntriesByName(absoluteURL).length;
}

promise_test(function() {
    return document.fonts.ready.then(function() {
        assert_equals(numberOfDownloads('/fonts/Ahem.ttf?pipe=trickle(d0.5)'), 1, 'first source should be loaded');
        assert_equals(numberOfDownloads('/fonts/Ahem.ttf?fallback-src'), 0, 'fallback source should not be loaded');
        assert_equals(numberOfDownloads('/fonts/Ahem.ttf?fallback-face'), 1, 'fallback font face should be loaded');
    });
}, "Fallback for font failure period");
</script>
