[webkit-dev] Another WPT bite

Ryosuke Niwa rniwa at webkit.org
Fri May 12 14:36:55 PDT 2017

On Fri, May 12, 2017 at 2:10 PM, Simon Fraser <simon.fraser at apple.com> wrote:
> On May 12, 2017, at 12:04 PM, Alexey Proskuryakov <ap at webkit.org> wrote:
> 12 мая 2017 г., в 11:52, Ben Kelly <ben at wanderview.com> написал(а):
> On Fri, May 12, 2017 at 2:26 PM, Rick Byers <rbyers at chromium.org> wrote:
>> On Fri, May 12, 2017 at 2:06 PM, Alexey Proskuryakov <ap at webkit.org>
>> wrote:
>>> 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
>> effort.
>> 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 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.
> FWIW, mozilla also treats WPT as first class tests.  We're not actively
> moving old tests to WPT like google, but all new tests (at least in DOM) are
> being written in WPT.  Of course, we do have exceptions for some tests that
> require gecko-specific features (forcing GC, etc).
> We don't have a concept of "first class", but I hope that when choosing
> between looking into a simple test that was added for a known important bug,
> and looking into an imported test whose importance is unclear, any WebKit
> engineer will pick the former. And since no one can fix all the things, such
> prioritization makes imported tests less effective.
> I just ran into a classic example of how a WPT incurred more overhead. I
> made a code change that broke
> LayoutTests/imported/w3c/web-platform-tests/cssom-view/elementFromPoint.html.
> I tried loading it in Safari and it doesn't run the test code because it
> can't find /resources/testharness.js when loaded from a local file.
> So then I have to figure out how to fire up the WPT server
> (run-webkit-httpd), then figure out which host to use (localhost or
> and which port, and finally to figure out the right path to the
> test.
> There's no reason this test should not work when loaded from file://.

This is an issue we can solve. We can rewrite link elements to use
relative path so that you can just open in the browser.
It's something we've wanted to do but haven't gotten around to yet.

- R. Niwa

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