LayoutTests/webgl/webgl2-rendering-context-obtain.html

<div id="result">PASS if a "webgl2" context can be obtained.</div>
<script>
if (window.testRunner)
    testRunner.dumpAsText();

if (!(document.createElement("canvas").getContext("webgl2") instanceof WebGL2RenderingContext))
    document.getElementById("result").innerHTML = "FAIL";
</script>