firefox/testing/web-platform/tests/html/canvas/resources/canvas-tests.js

function _valToString(val)
{
    if (val === undefined || val === null)
        return '[' + typeof(val) + ']';
    return val.toString() + '[' + typeof(val) + ']';
}

function _assert(cond, text)
{
    assert_true(!!cond, text);
}

function _assertSame(a, b, text_a, text_b)
{
    var msg = text_a + ' === ' + text_b + ' (got ' + _valToString(a) +
              ', expected ' + _valToString(b) + ')';
    assert_equals(a, b, msg);
}

function _assertDifferent(a, b, text_a, text_b)
{
    var msg = text_a + ' !== ' + text_b + ' (got ' + _valToString(a) +
              ', expected not ' + _valToString(b) + ')';
    assert_not_equals(a, b, msg);
}


function _getPixel(canvas, x,y)
{
    var ctx = canvas.getContext('2d');
    var imgdata = ctx.getImageData(x, y, 1, 1);
    return [ imgdata.data[0], imgdata.data[1], imgdata.data[2], imgdata.data[3] ];
}

function _assertPixel(canvas, x, y, r, g, b, a)
{
    var c = _getPixel(canvas, x,y);
    assert_equals(c[0], r, 'Red channel of the pixel at (' + x + ', ' + y + ')');
    assert_equals(c[1], g, 'Green channel of the pixel at (' + x + ', ' + y + ')');
    assert_equals(c[2], b, 'Blue channel of the pixel at (' + x + ', ' + y + ')');
    assert_equals(c[3], a, 'Alpha channel of the pixel at (' + x + ', ' + y + ')');
}

function _assertPixelApprox(canvas, x, y, r, g, b, a, tolerance)
{
    var c = _getPixel(canvas, x,y);
    assert_approx_equals(c[0], r, tolerance, 'Red channel of the pixel at (' + x + ', ' + y + ')');
    assert_approx_equals(c[1], g, tolerance, 'Green channel of the pixel at (' + x + ', ' + y + ')');
    assert_approx_equals(c[2], b, tolerance, 'Blue channel of the pixel at (' + x + ', ' + y + ')');
    assert_approx_equals(c[3], a, tolerance, 'Alpha channel of the pixel at (' + x + ', ' + y + ')');
}

function _assertMatricesApproxEqual(matA, matB)
{
  A = matA.toFloat32Array();
  B = matB.toFloat32Array();
  assert_equals(A.length, B.length);
  for (var i = 0; i < A.length; i++) {
    assert_approx_equals(A[i], B[i], 10e-6);
  }
}

function rad2deg(angle_in_radians) {
  return angle_in_radians / Math.PI * 180;
}

function deg2rad(angle_in_degrees) {
  return angle_in_degrees / 180 * Math.PI;
}

let _deferred = false;

function deferTest() {
  _deferred = true;
}

function _addTest(testFn, attributes={})
{
    on_event(window, "load", function()
    {
        t.step(function() {
            var canvas = document.getElementById('c');
            var ctx = canvas.getContext('2d', attributes);
            t.step(testFn, window, canvas, ctx);
        });

        if (!_deferred) {
            t.done();
        }
    });
}

function _assertGreen(ctx, canvasWidth, canvasHeight)
{
    var testColor = function(d, idx, expected) {
        assert_equals(d[idx], expected, "d[" + idx + "]", String(expected));
    };
    var imagedata = ctx.getImageData(0, 0, canvasWidth, canvasHeight);
    var w = imagedata.width, h = imagedata.height, d = imagedata.data;
    for (var i = 0; i < h; ++i) {
        for (var j = 0; j < w; ++j) {
            testColor(d, 4 * (w * i + j) + 0, 0);
            testColor(d, 4 * (w * i + j) + 1, 255);
            testColor(d, 4 * (w * i + j) + 2, 0);
            testColor(d, 4 * (w * i + j) + 3, 255);
        }
    }
}

function addCrossOriginYellowImage()
{
    var img = new Image();
    img.id = "yellow.png";
    img.className = "resource";
    img.src = get_host_info().HTTP_REMOTE_ORIGIN + "/images/yellow.png";
    document.body.appendChild(img);
}

function addCrossOriginRedirectYellowImage()
{
    var img = new Image();
    img.id = "yellow.png";
    img.className = "resource";
    img.src = get_host_info().HTTP_ORIGIN + "/common/redirect.py?location=" +
        get_host_info().HTTP_REMOTE_ORIGIN + "/images/yellow.png";
    document.body.appendChild(img);
}

function forEachCanvasSource(crossOriginUrl, sameOriginUrl, callback) {
  function makeImage() {
    return new Promise((resolve, reject) => {
      const image = new Image();
      image.onload = () => resolve(image);
      image.onerror = reject;
      image.src = crossOriginUrl + "/images/red.png";
    });
  }

  const arguments = [
    {
      name: "cross-origin HTMLImageElement",
      factory: makeImage,
    },

    {
      name: "cross-origin SVGImageElement",
      factory: () => {
        return new Promise((resolve, reject) => {
          const image = document.createElementNS("http://www.w3.org/2000/svg", "image");
          image.onload = () => resolve(image);
          image.onerror = reject;
          image.setAttribute("externalResourcesRequired", "true");
          image.setAttributeNS("http://www.w3.org/1999/xlink", 'xlink:href', crossOriginUrl + "/images/red.png");
          document.body.appendChild(image);
        });
      },
    },

    {
      name: "cross-origin HTMLVideoElement",
      factory: () => {
        return new Promise((resolve, reject) => {
          const video = document.createElement("video");
          video.oncanplaythrough = () => resolve(video);
          video.preload = "auto";
          video.onerror = reject;
          video.src = getVideoURI(crossOriginUrl + "/media/movie_300");
        });
      },
    },

    {
      name: "redirected to cross-origin HTMLVideoElement",
      factory: () => {
        return new Promise((resolve, reject) => {
          const video = document.createElement("video");
          video.oncanplaythrough = () => resolve(video);
          video.preload = "auto";
          video.onerror = reject;
          video.src = "/common/redirect.py?location=" + getVideoURI(crossOriginUrl + "/media/movie_300");
        });
      },
    },

    {
      name: "redirected to same-origin HTMLVideoElement",
      factory: () => {
        return new Promise((resolve, reject) => {
          const video = document.createElement("video");
          video.oncanplaythrough = () => resolve(video);
          video.preload = "auto";
          video.onerror = reject;
          video.src = crossOriginUrl + "/common/redirect.py?location=" + getVideoURI(sameOriginUrl + "/media/movie_300");
        });
      },
    },

    {
      name: "unclean HTMLCanvasElement",
      factory: () => {
        return makeImage().then(image => {
          const canvas = document.createElement("canvas");
          const context = canvas.getContext("2d");
          context.drawImage(image, 0, 0);
          return canvas;
        });
      },
    },

    {
      name: "unclean ImageBitmap",
      factory: () => {
        return makeImage().then(createImageBitmap);
      },
    },
  ];

  for (let { name, factory } of arguments) {
    callback(name, factory);
  }
}