ses.length; ++i) {
  asyncTests[i].step(() => {
    const backgroundSizePx = parseBackgroundSizeInPx(elements[i], '::' + testCases[i]);
    assert_less_than(backgroundSizePx, 24);
  });
}

// Insert custom font into style sheet and load it
const customFont = new FontFace('custom font', 'url(/fonts/Ahem.ttf)');
document.fonts.add(customFont);

// After loading custom font, tests should be rendered with the custom font,
// which is Ahem, and have a '1ch' measurement that equals 25px.
customFont.load().then(
 