readbackFromWebGPUCanvas:transferToImageBitmap_unconfigured_nonzero_size expects opaque black image (alpha == 255)

[jamienicol]

I'm looking at making the above test pass in Firefox (https://bugzilla.mozilla.org/show_bug.cgi?id=1948580)

I can see the test expects the returned bitmaps pixels to have an alpha value of 255. But looking at the spec (steps 1 to 3) it seems to me the returned image should be transparent black, ie alpha == 0, as the canvas is unconfigured.

Does the CTS need updated, or am I misreading the spec?