Updates on canvas backreference for canvas rendering contexts

third_party/WebKit/LayoutTests/fast/canvas/rendering-contexts-back-references.html

+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<script>
+var tests = [];
+function test_back_ref(canvas, context, anotherCanvas, message)
+{
+    assert_equals(context.canvas, canvas);
+    context.canvas = anotherCanvas;
+    assert_not_equals(context.canvas, anotherCanvas, message);
+}
+
+// Back reference to html canvas
+var htmlCanvas1 = document.createElement("canvas");
+tests.push(["Test back references to html canvas for CanvasRenderingContext2D",
+        htmlCanvas1, htmlCanvas1.getContext("2d"), document.createElement("canvas"), "ctx2d.canvas is read-only."]); 
+
+var htmlCanvas2 = document.createElement("canvas");
+tests.push(["Test back references to html canvas for WebglRenderingContext",
+        htmlCanvas2, htmlCanvas2.getContext("webgl"), document.createElement("canvas"), "webglCtx.canvas is read-only."]); 
+
+var htmlCanvas3 = document.createElement("canvas");
+tests.push(["Test back references to canvas for ImageBitmapRenderingContext",
+        htmlCanvas3, htmlCanvas3.getContext("bitmaprenderer"), document.createElement("canvas"), "bitmaprenderer.canvas is read-only."]);
+
+// Back reference to Offscreen canvas
+var offscreenCanvas1 = new OffscreenCanvas(10, 10);
+tests.push(["Test back references to offscreencanvas for OffscreenCanvasRenderingContext2D",
+        offscreenCanvas1, offscreenCanvas1.getContext("2d"), new OffscreenCanvas(10, 10), "ctx2d.canvas is read-only."]);
+
+var offscreenCanvas2 = new OffscreenCanvas(10, 10);
+tests.push(["Test back references to offscreencanvas for WebglRenderingContext",
+        offscreenCanvas2, offscreenCanvas2.getContext("webgl"), new OffscreenCanvas(10, 10), "webgl.canvas is read-only."]);
+
+generate_tests(test_back_ref, tests);

[Justin Novosad, 2016/08/11 17:37:57]

You are not using the test pattern optimally. The idea is to use generate_tests
in a way that maximizes readability and maintainability. Something like this
(untested code):

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 works.");
    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>