Re: Specifications with matching test APIs

Thanks for summarizing, Vincent, is, I believe, the most well-defined
such API so far. Perhaps a next good step would be to prepare a PR that
adds one such test to to make it all
very concrete, to see what issues come up?

On Tue, Jun 13, 2017 at 7:52 PM Vincent Scheib <> wrote:

> Related to this thread "Specifications with matching test APIs"
> <>
> and the earlier thread "UserAgent-specific files in Web Platform Tests"
> <>
> This is a summary of a call discussing web platform testing with “Test
> APIs” including James Graham (Mozilla) and Philip Jägenstedt, Reilly Grant,
> Vincent Scheib (Google).
> Web Bluetooth, WebUSB, and WebVR are actively seeking to develop web
> platform tests with new requirements compared to existing tests. Complex
> state must be configured for these features to be tested, e.g. fake
> bluetooth devices. “Test APIs” are proposed as being paired with
> specifications.
> Concerns raised and discussed include:
> A) With new testing patterns we may develop unexpected influence on future
> implementations. Particularly risky when only a small number of developers
> are influencing the API. E.g. WebUSB which doesn’t yet have other
> implementations.
> B) WebDriver already operates at a high level, helping avoid test APIs
> being too implementation specific.
> C) Test APIs that don’t work with browser’s standard shipping versions may
> be a problem. E.g. they won’t run with web-developer focused testing
> infrastructure, BrowserStack, Sauce, etc. And, they’re harder to run
> manually.
> D) Our primary goal is to have conforming web browser implementations.
> Considering the goal of “Testing APIs should work for web-app developers”
> is lower priority.
> Recommendations:
> Test APIs should clearly indicate their purpose and scope:
> - They are intended only for WPT. This means test APIs can be modified
> more freely if a later implementation discovers limitations in the testing
> API. We do not want additional resistance to API change due to e.g. web app
> developers using the test API.
> - Test APIs should be designed carefully to only use concepts from the
> feature being tested, and not the details of the implementation. E.g.
> garbage collection, implementation specific feature details, synchronous
> responses, etc.
> Full notes
> <>
> .
> On Wed, May 3, 2017 at 8:55 AM, Philip Jägenstedt <>
> wrote:
>> On Mon, Apr 24, 2017 at 4:33 PM James Graham <>
>> wrote:
>>> On 22/04/17 02:28, Reilly Grant wrote:
>>> > On Fri, Apr 21, 2017 at 6:11 PM Rick Byers <>
>>> wrote:
>>> >
>>> >> Thanks Reilly, I support continuing to move in this direction!
>>> >>
>>> >> Are you planning in shipping this API in release Chrome builds behind
>>> a
>>> >> flag?  I think it would be reasonable to modify the WPT infrastructure
>>> >> (stability_checker, dashboard) to pass a --enable-testing-apis flag
>>> >> (although we might need to consider the security implications of that
>>> for
>>> >> the WPT infrastructure running potentially untrusted test patches).
>>> But I
>>> >> don't think we'd want to use content_shell (or even Chromium builds)
>>> in
>>> >> that infrastructure - at least not in place of Chrome builds.
>>> >>
>>> >
>>> > The ability to override the Mojo services provided to the renderer
>>> from the
>>> > renderer itself (which is how Chromium's polyfill for this API is
>>> > implemented) is only available in content_shell when the
>>> --run-layout-test
>>> > parameter is passed. There have been discussions with the Mojo team
>>> about
>>> > making this available in production Chrome builds when a flag is
>>> enabled.
>>> > It would have to be a flag which displays the "unsupported flag,
>>> security
>>> > and stability will suffer" infobar because it effectively allows
>>> arbitrary
>>> > JavaScript to run with the privileges of the renderer.
>>> This seems like:
>>> * An API with unclear vendor buy-in.
>>> * An test API that is (effectively) not available outside Chromium CI
>>> (although it's possible to get contentshell builds it's not a bad
>>> approximation to assume that no one will).
>>> So I'm pretty worried about this approach. It seems like there's a high
>>> chance that the test api will encode Blink implementation details, we
>>> will struggle to run the tests outside your CI, and web developers who
>>> want to test their USB-using website will be left to search for a
>>> different solution.
>> I think it's probably true that there are ways of depending on
>> implementation details with a testing API that are unlikely/impossible
>> using a WebDriver extension, but with either approach it would be very
>> surprising if the tests didn't need any adjustment when the second
>> implementer starts running them. As long as the effort to find and fix such
>> problems is much lower than writing tests from scratch, is it not still a
>> net win? It seems likely to me that this would be the case, especially when
>> making a conscious effort to define a testing API that doesn't depend on
>> implementation details.
>> Until there is a second implementer showing public interest, would it
>> help to contain tests like this to webusb/chromium/ or similar?

Received on Wednesday, 14 June 2017 08:24:00 UTC