chromium/third_party/blink/web_tests/external/wpt/html/rendering/non-replaced-elements/the-fieldset-and-legend-elements/fieldset-flexbox.html

<!DOCTYPE html>
<title>fieldset and CSS Flexbox</title>
<script src=/resources/testharness.js></script>
<script src=/resources/testharnessreport.js></script>
<style>
#test, #ref, #test-inline, #ref-inline {
  display: flex;
  justify-content: space-around;
  margin: 0;
  padding: 0;
  border: none
}
#test-inline, #ref-inline { display: inline-flex }
legend {
  float: left; /* Makes it not the "rendered legend" */
  padding: 0;
}
</style>
<fieldset id=test>
 <legend>1</legend>
 <div>2</div>
 <div>3</div>
 <div>4</div>
 <div>5</div>
 <div>6</div>
 <div>7</div>
 <div>8</div>
 <div>9</div>
</fieldset>
<hr>
<div id=ref>
 <legend>1</legend>
 <div>2</div>
 <div>3</div>
 <div>4</div>
 <div>5</div>
 <div>6</div>
 <div>7</div>
 <div>8</div>
 <div>9</div>
</div>
<hr>
<fieldset id=test-inline>
 <legend>1</legend>
 <div>2</div>
 <div>3</div>
 <div>4</div>
 <div>5</div>
 <div>6</div>
 <div>7</div>
 <div>8</div>
 <div>9</div>
</fieldset>
<div id=ref-inline>
 <div>1</div>
 <div>2</div>
 <div>3</div>
 <div>4</div>
 <div>5</div>
 <div>6</div>
 <div>7</div>
 <div>8</div>
 <div>9</div>
</div>
<script>
  test(() => {
    const testElm = document.getElementById('test');
    const refElm = document.getElementById('ref');
    assert_equals(getComputedStyle(testElm).height,
                  getComputedStyle(refElm).height, 'height');
    assert_equals(testElm.querySelector('legend').offsetTop,
                  testElm.querySelector('div').offsetTop, 'offsetTop')
  }, "Flex");

  test(() => {
    const testElm = document.getElementById('test-inline');
    const refElm = document.getElementById('ref-inline');
    assert_equals(getComputedStyle(testElm).height,
                  getComputedStyle(refElm).height, 'height');
    assert_equals(testElm.querySelector('legend').offsetTop,
                  testElm.querySelector('div').offsetTop, 'offsetTop')

  }, "Inline flex");

test(() => {
  const testElm = document.getElementById('test');
  testElm.style.flexDirection = 'row';
  const item0 = testElm.querySelectorAll('div')[0];
  const item1 = testElm.querySelectorAll('div')[1];
  assert_equals(item0.offsetTop, item1.offsetTop);

  testElm.style.flexDirection = 'column';
  assert_true(item0.offsetTop < item1.offsetTop);
}, "Dynamic change of flex-direction");
</script>