Improve Test Filter Management

[sol-loup]

PR: Improve Test Filter Management with AbstractWPUnitTestWithSafeFiltering

This PR addresses a common source of test flakiness by implementing proper WordPress filter management in our test suite.

The Problem

Sometimes when testing, you want to override the behavior of a global function. This can be done using a wordpress primitive called add_filter

While this can be helpful for mocking deep functionality, these filters present a challenge when testing across hundreds of files:

1. Filter Leakage: When add_filter() is used in tests without proper cleanup, filters persist between tests, causing unexpected behavior and interdependencies.

2. Incomplete Cleanup: Manual filter removal is error-prone and often forgotten, especially when tests fail before reaching teardown code.

3. Overly Aggressive Cleanup: Using remove_all_filters() is dangerous as it removes ALL filters for a hook, including those added by WordPress core or other plugins, potentially breaking functionality in subsequent tests.

Solution Proposed by this PR

The AbstractWPUnitTestWithSafeFiltering class provides:

• A add_filter_with_safe_teardown() method that tracks all added filters
• Automatic cleanup in tearDown() that only removes filters added by the current test
• The ability to remove specific filters early with teardown_safely_immediately()
• A category-specific cleanup method with teardown_callback_category_safely() -- allowing you to safely wipe out all test-related filters for 'event_type_A' without affecting B or C.

Changes

• Introduced AbstractWPUnitTestWithSafeFiltering with above functionality.
• Updated WCFacebookCommerceIntegrationTest, fbproductTest, WPMLTest, and FeedUploadUtilsTest to extend AbstractWPUnitTestWithSafeFiltering
• Replaced all add_filter() calls with add_filter_with_safe_teardown()
• in some special cases (per-test), replaced remove_all_filters with appropriate teardown calls
• In most cases, rely on default "invisible" safe teardown behavior

Testing Performed

• Ran updated test suit using phpunit -- all succeeded.

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@sol-loup has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

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@sol-loup merged this pull request in d61751e.