sousa-gecko/testing/web-platform/tests/container-timing/resources/container-timing-helpers.js

function checkContainerEntry(entry, identifier, last_element_id, beforeRender) {
  assert_equals(entry.entryType, 'container');
  assert_equals(entry.name, 'container-paints');
  assert_equals(entry.identifier, identifier, 'identifier does not match');
  if (last_element_id != null) {
    assert_equals(entry.lastPaintedElement.id, last_element_id);
  }

  assert_equals(entry.duration, 0, 'duration should be 0');
  assert_greater_than_equal(
      entry.firstRenderTime, beforeRender,
      'firstRenderTime greater than beforeRender');
  assert_greater_than_equal(
      entry.startTime, entry.firstRenderTime,
      'startTime greater than beforeRender');
  assert_greater_than_equal(
      performance.now(), entry.startTime, 'startTime bound by now()')

  // PaintTimingMixin
  if ("presentationTime" in entry && entry.presentationTime !== null) {
    assert_greater_than(entry.presentationTime, entry.paintTime);
    assert_equals(entry.presentationTime, entry.startTime);
  } else {
    assert_equals(entry.startTime, entry.paintTime);
  }
}

function checkContainerSize(entry, size) {
  assert_equals(entry.size, size);
}

function checkContainerIntersectionRect(entry, expected, description = '') {
  assert_equals(
      entry.intersectionRect.left, expected[0], 'left of rect ' + description);
  assert_equals(
      entry.intersectionRect.right, expected[1],
      'right of rect ' + description);
  assert_equals(
      entry.intersectionRect.top, expected[2], 'top of rect ' + description);
  assert_equals(
      entry.intersectionRect.bottom, expected[3],
      'bottom of rect ' + description);
}

// The test wait methods use ElementTiming if available (that should finish
// the tests faster), or use a 2 seconds timeout as a fallback.

// To try the non ElementTiming fallback just set this variable to false.
const is_element_timing_available = !!window.PerformanceElementTiming;

function setupElementTimingWait(func, parent) {
  const finish_observer = new PerformanceObserver((entryList) => {
    finish_observer.disconnect();
    requestAnimationFrame(() => {
      func();
    });
  });

  finish_observer.observe({entryTypes: ['element']});

  const finish_img = document.createElement('img');
  finish_img.src = '/container-timing/resources/square100.png';
  finish_img.setAttribute('elementtiming', '');
  parent.appendChild(finish_img);
}

function setupTimeoutWait(t, func) {
  t.step_timeout(() => {
    func();
  }, 2000);
}

function setupWait(t, parent, func) {
  if (is_element_timing_available) {
    setupElementTimingWait(func, parent);
  } else {
    setupTimeoutWait(t, func);
  }
}

function waitAfterTest(t, parent, func) {
  requestAnimationFrame(() => {
    requestAnimationFrame(() => {
      setupWait(t, parent, func);
    });
  });
}