[huzaifaalmesbah]

Description

Adds tests for activate_plugin(). The existing tests only call it through activate_plugins() for a single plugin; its validation, hooks, redirect, output check and network activation had no direct tests.

The tests create a temporary plugin for each test (a plugin file is only loaded once per process), stop the redirect through the wp_redirect filter, and restore $_GET. They cover:

• plugin_not_found for a plugin that is not installed, and plugin_php_incompatible for unmet requirements, without changing the active plugins;
• the plugin being added to the sorted active plugins, and activate_plugin, activate_{$plugin} and activated_plugin firing in order with their arguments;
• a full path with surrounding whitespace being reduced to the plugin basename;
• no hooks in silent mode;
• nothing happening for a plugin that is already active, including no redirect;
• unexpected_output with the output as error data when loading the plugin prints something, while the plugin stays activated;
• the redirect to the error URL with an _error_nonce;
• on multisite, network-wide activation (with $_GET['networkwide']), a network-only plugin always being activated network-wide, and a network-active plugin keeping its activation time.

Removing or changing each branch of the function makes at least one test fail on single site or multisite.

One case is left out on multisite: activate_plugin() calls is_network_only_plugin() before validate_plugin(), so a plugin that is not installed raises a file_get_contents() warning before the plugin_not_found error is returned. That can be handled in its own ticket.

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_Admin_Includes_Plugin_ActivatePlugin
2. Run them on multisite:
   npm run test:php -- --filter Tests_Admin_Includes_Plugin_ActivatePlugin -c tests/phpunit/multisite.xml
3. Run them in random order:
   npm run test:php -- --filter Tests_Admin_Includes_Plugin_ActivatePlugin --order-by=random
4. Run the plugins group:
   npm run test:php -- --group plugins
5. Run PHPCS on the test file:
   node ./tools/local-env/scripts/docker.js run --rm php ./vendor/bin/phpcs tests/phpunit/tests/admin/includes/plugin/activatePlugin.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.

[github-actions]

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Props huzaifaalmesbah, mukesh27.

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[mukeshpanchal27]

The assertions match the source, and CI passes. One note about fixture cleanup inline.

[mukeshpanchal27]

In core tests, WP_PLUGIN_DIR is tests/phpunit/data/plugins, which is a tracked directory. If a run stops partway, such as on a fatal error or Ctrl+C, tear_down() never runs and this fixture folder stays there. The slug comes from a counter that starts at 1 again on the next run, so mkdir() fails on the same folder name. So every test in the class fails here until someone deletes the folder by hand. The leftover also shows up in git status.

Could this helper, or set_up(), remove a leftover folder first? #14600 already does this: its remove_plugin() helper runs in both set_up() and tear_down().

[huzaifaalmesbah]

Good catch, thanks! Added a remove_plugin() helper that clears a leftover folder before mkdir() and in tear_down(), in b888f06. I checked it with a leftover folder in place: the old code failed and the new code passes.