servo/tests/wpt/web-platform-tests/css/support/interpolation-testcommon.js

'use strict';
function test_interpolation(settings, expectations) {
  // Returns a timing function that at 0.5 evaluates to progress.
  function timingFunction(progress) {
    if (progress === 0)
      return 'steps(1, end)';
    if (progress === 1)
      return 'steps(1, start)';
    var y = (8 * progress - 1) / 6;
    return 'cubic-bezier(0, ' + y + ', 1, ' + y + ')';
  }

  test(function(){
    assert_true(CSS.supports(settings.property, settings.from), 'From value "' + settings.from + '" is supported by ' + settings.property);
    assert_true(CSS.supports(settings.property, settings.to), 'To value "' + settings.to + '" is supported by ' + settings.property);
  }, '"' + settings.from + '" and "' + settings.to + '" are valid ' + settings.property + ' values');

  for (var i = 0; i < expectations.length; ++i) {
    var progress = expectations[i].at;
    var expectation = expectations[i].expect;
    var animationId = 'anim' + i;
    var targetId = 'target' + i;
    var referenceId = 'reference' + i;
    test(function(){
      assert_true(CSS.supports(settings.property, expectation), 'Expectation value "' + expectation + '" is supported by ' + settings.property);

      var stylesheet = document.createElement('style');
      stylesheet.textContent =
        '#' + targetId + ' {\n' +
        '  animation: 2s ' + timingFunction(progress) + ' -1s paused ' + animationId + ';\n' +
        '}\n' +
        '@keyframes ' + animationId + ' {\n' +
        '  0% { ' + settings.property + ': ' + settings.from + '; }\n' +
        '  100% { ' + settings.property + ': ' + settings.to + '; }\n' +
        '}\n' +
        '#' + referenceId + ' {\n' +
        '  ' + settings.property + ': ' + expectation + ';\n' +
        '}\n';
      document.head.appendChild(stylesheet);

      var target = document.createElement('div');
      target.id = targetId;
      document.body.appendChild(target);

      var reference = document.createElement('div');
      reference.id = referenceId;
      document.body.appendChild(reference);
      reference.style = '';

      assert_equals(getComputedStyle(target)[settings.property], getComputedStyle(reference)[settings.property]);
    }, (settings.test_prefix ? settings.test_prefix : "") +
       'Animation between "' + settings.from + '" and "' + settings.to +
       '" at progress ' + progress);
  }
}

function test_no_interpolation(settings) {
  var expectatFrom = [-1, 0, 0.4].map(function (progress) {
    return {at: progress, expect: settings.from};
  });
  var expectatTo = [0.6, 1, 2].map(function (progress) {
    return {at: progress, expect: settings.to};
  });

  test_interpolation(settings, expectatFrom.concat(expectatTo));
}