[webkit-dev] Another WPT bite

Rick Byers rbyers at chromium.org
Fri May 12 11:26:40 PDT 2017

On Fri, May 12, 2017 at 2:06 PM, Alexey Proskuryakov <ap at webkit.org> wrote:

> 9 мая 2017 г., в 11:27, Simon Fraser <simon.fraser at apple.com> написал(а):
> Another consideration here is "would my test be useful for other browser
> vendors". I don't think the answer is a unanimous "yes", so I think we
> should only use WPT for tests that will think are worth sharing.
> Since imported WPT tests are very flaky, and are not necessarily written
> to defend against important regressions, investigating issues with them is
> relatively lower priority than investigating issues observed with WebKit
> tests. So I would recommend not mixing tests for WebKit regressions with
> WPT tests - if your test eventually ends up in LayoutTests/imported, it
> will become a lot less effective.

FWIW this is absolutely NOT how we're treating this in chromium.  If this
is how things end up in practice then we will have failed massively in this

We figure if we want the web to behave consistently, we really have no
choice but to treat web-platform-tests as first class with all the
discipline we give to our own tests.  As such we are actively moving
<https://codereview.chromium.org/2877673004> many of our LayoutTests to
web-platform-tests and depending entirely on the regression prevention they
provide us from there.  Obviously there will be hiccups, but because our
product quality will depend on web-platform-tests being an effective and
non-flaky testsuite (and because we're starting to require most new
features have web-platform-tests before they ship), I'm confident that
we've got the incentives in place to lead to constant ratcheting up the
engineering discipline and quality of the test suite.

Pragmatically to get there incrementally we're applying different policies
to different WPT directories.  Eg. for some directories if a WPT import
results in new failures we probably won't care enough to prioritize
investigating them.  But for many (which map to a feature team on the hook
for quality in that area) we'll treat it with the same priority as a newly
failing LayoutTest on our bots.

Of course the WebKit project might have a higher test quality bar than the
chromium project, so the right choice could be incredibly different for you
than for us.  But should you choose to treat WPT as a first-class test
suite for your project, we're committed to working together to make it work
well in practice for all of us.  We figure that in the long-run, if we
shift investments from our own LayoutTests to web-platform-tests, even
though there will be some additional costs and risks, it'll eventually lead
to both lower testing costs and higher product quality because we're
leveraging the work of spec editors like Anne and other implementors who
are also working to improve the test suite.

Using the complicated harness has a similar consequence - if you use any
> WPT goodies like templates or server side scripts, the cost of
> investigating issues on the test increases, and makes the test less
> valuable.
> I don't know if there is any way to adopt WPT that won't make testing less
> effective. WPT tests may be useful in very rare cases, where we actively
> want to communicate certain subtle behavior details to other vendors - but
> even so, I imagine that other vendors may not put high priority on those,
> for the same reasons.
> - Alexey
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