See https://bugzilla.mozilla.org/show_bug.cgi?id=1076583#c26

I suspect that test was written against an earlier revision of the spec (before the spec had a concept of pending request etc). The test also seems wrong (maybe because it was moved?) here

img.src = '../images/red.png';

because that ends up being http://web-platform.test:8000/2dcontext/images/red.png which is a 404...

cc @jdm