mozilla-release/testing/web-platform/tests/resource-timing/buffer-full-store-and-clear-during-callback.html

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<head onload>
<meta charset="utf-8" />
<title>This test validates the behavior of read and clear operation in onresourcetimingbufferfull callback of resource timing.</title>
<link rel="author" title="Intel" href="http://www.intel.com/" />
<link rel="help" href="http://www.w3.org/TR/resource-timing/#performanceresourcetiming"/>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/buffer-full-utilities.js"></script>
</head>
<body>
<script>
const resource_timing_buffer_size = 1;
let global_buffer = [];
let eventFired = false;

setup(() => {
    clearBufferAndSetSize(resource_timing_buffer_size);
    let store_and_clear = function() {
        const entryList = performance.getEntriesByType('resource');
        entryList.forEach(function (entry) {
            global_buffer.push(entry);
        });
        performance.clearResourceTimings();
        eventFired = true;
    }
    performance.addEventListener('resourcetimingbufferfull', store_and_clear);
});

let overflowTheBuffer = () => {
    return new Promise(resolve => {
        // This resource overflows the entry buffer, and goes into the secondary buffer.
        appendScript('resources/empty_script.js', resolve);
    });
};

let testThatBufferContainsTheRightResources = () => {
    let entries = performance.getEntriesByType('resource');
    assert_equals(entries.length, 1,
                  "Only the last entry should be stored in resource timing buffer since it's cleared once it overflows.");
    assert_equals(global_buffer.length, 1, '1 resource timing entry should be moved to global buffer.');
    assert_true(global_buffer[0].name.includes('empty.js'), "empty.js is in the global buffer");
    assert_true(entries[0].name.includes('empty_script.js'), "empty_script.js is in the entries buffer");
};

promise_test(async () => {
    await fillUpTheBufferWithSingleResource("resources/empty.js");
    await overflowTheBuffer();
    await waitForEventToFire();
    testThatBufferContainsTheRightResources();
}, "Test that entries overflowing the buffer trigger the buffer full event, can be stored, and find themselves in the primary buffer after it's cleared.");
</script>
</body>
</html>