Tests: Add unit test coverage for WP_Widget_Meta

[huzaifaalmesbah]

Description

Adds a test class for WP_Widget_Meta, which had no tests. The tests cover the registration settings, the title shown by widget() (custom, default and falsy values), the widget_title filter arguments and the omitted title wrapper when it returns an empty string, the <nav> wrapper and its aria-label for the html5 format and its absence for xhtml, the log in, feed and WordPress.org links for a logged-out visitor, the Site Admin and log out links for a logged-in user, the widget_meta_poweredby filter arguments and return value, and the wp_meta action. They also cover title sanitization in update(), that update() keeps the other settings of the old instance, and the escaped title field rendered by form().

This is a test-only change; no production code is modified.

Testing Instructions

1. Run the tests on single site:
   npm run test:php -- --filter 'Tests_Widgets_wpWidgetMeta'
2. Run them on multisite:
   npm run test:php -- --filter 'Tests_Widgets_wpWidgetMeta' -c tests/phpunit/multisite.xml
3. Run them in random order:
   npm run test:php -- --filter 'Tests_Widgets_wpWidgetMeta' --order-by=random
4. Run the whole group to confirm nothing else is affected:
   npm run test:php -- --group widgets
5. Run PHPCS on the test file:
   node ./tools/local-env/scripts/docker.js run --rm php ./vendor/bin/phpcs tests/phpunit/tests/widgets/wpWidgetMeta.php

Trac ticket: https://core.trac.wordpress.org/ticket/65819

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5.5
Used for: Brainstorming edge-case scenarios and drafting test boilerplate; test architecture, assertions, and local PHPUnit verification were written and validated by me.

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Props huzaifaalmesbah, rejaulalomkhan.

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[rejaulalomkhan]

Great work adding comprehensive test coverage for WP_Widget_Meta, @huzaifaalmesbah!

The suite nicely covers both logged-in and logged-out views, the wp_meta hook placement, and the widget_meta_poweredby filter.

A couple of minor observations:

1. In test_widget_displays_links_for_logged_in_user(), switching users with wp_set_current_user() can sometimes leak the authenticated state into subsequent tests if not reset in tear_down(). Calling wp_set_current_user( 0 ) in tear_down() might add an extra layer of test isolation.
2. For test_widget_displays_links_for_logged_out_visitor(), would it make sense to also assert that the Register link is displayed when users_can_register is 1?

Overall, the class structure is very clean and adheres well to Core conventions!