The test web-platform/tests/css/printing/page-size-009-print.html was integrated into our copy of WPT a week ago, marked as failing.

The test expects a 200px square page (sheet), followed by a 300px x 400px page (sheet). We don't implement mixed page sizes yet (bug 1836059) and I'm only just about to land the code to implement reorientation of sheets to match the orientation of pages (bug 1833244).

That latter bug (bug 1833244) only gets us part way to fixing this test but, by allowing sheet orientation to be switched to match page orientation, we end up with mismatched canvas orientations (dimensions) in nsDOMWindowUtils::CompareCanvases in the test harness, making it fail in a different way. The NS_ERROR_FAILURE that is returned there is thrown by the JS, causing the test to abort and be reported as TEST-UNEXPECTED-FAIL, despite failure (to pass) being expected anyway.

So in bug 1833244 I'm going to mark this test as disabled for now rather than expected: FAIL. Once we turn on bug 1836059 (mixed page sizes) this test should pass.

(In reply to Jonathan Watt [:jwatt] from comment #0)

Once we turn on bug 1836059 (mixed page sizes) this test should pass.

Looks like the test still doesn't pass, per https://wpt.fyi/results/css/printing/page-size-009-print.html?label=experimental

ni=jwatt to follow up here.

Testcase vs. reference case, for convenience:
https://wpt.live/css/printing/page-size-009-print.html
https://wpt.live/css/printing/page-size-009-print-ref.html

Looks like the test is expecting us to resolve vw and vh units against the size of the first page (including for content that lands on later pages that have different sizes); and we're failing to do that, I guess?