Initial focus assumption for tests

[jonathan-j-lee]

web-platform-tests/wpt@bef892c489 replaced window.open() + polling for opening testharness windows with the WebDriver "New Window" command, which doesn't run focusing steps. This inadvertently broke tests that implicitly relied on initial focus, such as:

• https://crrev.com/c/6341204
• https://wpt.fyi/results/navigation-api/focus-reset/change-focus-again-in-blur-during-intercept.html?label=master&label=experimental&aligned&view=interop&q=label%3Ainterop-2025-navigation
• Fix focus related failures due to URL bar being focused on launch wpt#56270

I think we should clarify and maybe document what (if any) initial focus target WPT guarantees. If we decide not to guarantee anything, each test will need to set up its own initial focus target.

As a point of comparison, the Marionette testharness implementation currently provides focus=True, which means "the opened window will be focused" (similar to the pre-bef892c489 WebDriver behavior).

[gsnedders]

Note there's both "system focus" and the HTML concept of "focused area of the document". We're presumably talking about the former, because every window has at least one document, each of which has its own focused area.

Also, FWIW, safaridriver currently grabs focuses far more often than the WebDriver spec expects or allows, thus why e.g. the above test passes in Safari, despite using the WebDriver executor.

The challenge for system focus, I think, is anyone trying to run the test in parallel. It would be nice here to avoid basically requiring that every test runs with system focus, because it means you can never correctly run tests in parallel — even ignoring all the other aspects of statefulness which make this difficult.

Do we know how many tests this affects?

How viable is it to just make each of these tests get focus via testdriver?

At least presently I don't think there's any way per-spec to get system focus to a specific window — and while web-platform-tests/wpt#56508 tries to do so via the click endpoint, I don't think that guarantees anything per spec