[css-text] Check interraction of tab-size, letter-spacing, word-spacing

[frivoal]

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[wpt-pr-bot]

Peer review is not required for CSS editors.

[frivoal]

@fantasai @kojiishi I think I got this right, but it's failing (differently) in all browsers, so I wouldn't mind a quick sanity-check review.

[fantasai]

Looks correct to me. However, I would not use the overlapping technique for this one if there's a problem with antialiasing. I'd just stack the references and say something like “There should be a blue square with perfectly smooth sides below.” or something, and make each one a 2:1 rectangle.

[frivoal]

Looks correct to me.

Cool.

However, I would not use the overlapping technique for this one if there's a problem with antialiasing. I'd just stack the references and say something like “There should be a blue square with perfectly smooth sides below.” or something, and make each one a 2:1 rectangle.

I'm actually going to disagree. With the technique your proposing, it's harder to be sure you're in the pass case. If the two halves really don't line up, then the failure will be clear. But if they do, this kind of tests/phrasing will encourage people to squint hard at the screen to try and decide whether the edges are sufficiently smooth... And if the positioning is off by less than 1px, neither nor variant nor mine are very good at catching that. But I'd consider that a matter of precision rather than correctness, and so I don't think this is something we should try to catch.

Anyway. Merging. If you feel strongly about that, let's open a new issue or PR to follow up.