chromium/src/third_party/blink/web_tests/fast/canvas/rendering-contexts-back-references.html

<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script>
function make_canvas(type)
{
    if (type == "html")
        return document.createElement("canvas");
    return new OffscreenCanvas(10, 10);
}

function test_back_ref(contextType, canvasType)
{
    var canvas = make_canvas(canvasType);
    var ctx = canvas.getContext(contextType);
    assert_equals(ctx.canvas, canvas, "Back reference to canvas should work.");
    var anotherCanvas = make_canvas(canvasType);
    ctx.canvas = anotherCanvas;
    assert_not_equals(ctx.canvas, anotherCanvas, "Canvas attribute is read only.");
}

generate_tests(test_back_ref, [
    ["2d context on html canvas",             "2d",             "html"],
    ["webgl context on html canvas",          "webgl",          "html"],
    ["bitmaprenderer context on html canvas", "bitmaprenderer", "html"],
    ["2d context on offscreen canvas",        "2d",             "offscreen"],
    ["webgl context on offscreen canvas",     "webgl",          "offscreen"],
]);
</script>