mozilla-release/testing/web-platform/tests/resource-timing/buffer-full-add-entries-during-callback.html

<!DOCTYPE HTML>
<html>
<head onload>
<meta charset="utf-8" />
<title>This test validates that synchronously adding entries in onresourcetimingbufferfull callback results in these entries being properly handled.</title>
<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;

setup(() => {
    // Get the browser into a consistent state.
    clearBufferAndSetSize(resource_timing_buffer_size);
});

let overflowTheBufferAndWaitForEvent = () => {
    return new Promise(resolve => {
        var add_entry = () => {
            performance.setResourceTimingBufferSize(resource_timing_buffer_size + 2);
            xhrScript("resources/empty.js?xhr");
            resolve();
        }
        performance.addEventListener('resourcetimingbufferfull', add_entry);
        // This resource overflows the entry buffer, and goes into the secondary buffer.
        appendScript('resources/empty_script.js');
    });
};

let testThatBufferContainsTheRightResources = () => {
    let entries = performance.getEntriesByType('resource');
    assert_equals(entries.length, 3,
                  'All entries should be stored in resource timing buffer since its increases size once it overflows.');
    assert_true(entries[0].name.includes('empty.js'), "empty.js is in the entries buffer");
    assert_true(entries[1].name.includes('empty_script.js'), "empty_script.js is in the entries buffer");
    assert_true(entries[2].name.includes('empty.js?xhr'), "empty.js?xhr is in the entries buffer");
};

promise_test(async () => {
    await fillUpTheBufferWithSingleResource("resources/empty.js");
    await overflowTheBufferAndWaitForEvent();
    await waitForNextTask();
    testThatBufferContainsTheRightResources();
}, "Test that entries synchronously added to the buffer during the callback don't get dropped if the buffer is increased");
</script>
</body>
</html>