LayoutTests/fast/canvas/change-context.html

This test ensures that changing the context does not crash.
<canvas id="canvas"></canvas><br />
<script>
if (window.testRunner)
    testRunner.dumpAsText();

var canvas = document.getElementById("canvas");
var ctx1 = canvas.getContext("2d");
var ctx2 = canvas.getContext("");
ctx1.save();

canvas.parentNode.removeChild(canvas);

if (window.GCController)
    GCController.collect();
    
ctx1.save();

</script>