Add GitHub Actions workflow to validate PHPUnit test file conventions.

[pbearne]

Trac ticket: https://core.trac.wordpress.org/ticket/65208

Description

Adds a dedicated GitHub Actions workflow (.github/workflows/validate-phpunit-cleanup-pr.yml) to automatically validate that PHPUnit test files added or updated in pull requests comply with the core test modernization specification (#65208, #53010).

Automated Checks Performed:

• File Path Hierarchy: Validates that test files adhere to the standardized directory structure under tests/phpunit/tests/:
  • For class methods: tests/phpunit/tests/wp-[includes|admin]/[SubFolder/]*Class_Under_Test/FunctionUnderTest[OptionalSubsetIndicator]Test.php
  • For procedural functions: tests/phpunit/tests/wp-[includes|admin]/[SubFolder/]*Functions_FileName/FunctionUnderTest[OptionalSubsetIndicator]Test.php
• Namespace Compliance: Ensures all test files declare a valid PSR-4 namespace starting with WordPress\Tests\... that strictly maps to the directory structure.
• Class Naming & Granularity:
  • Enforces single-class-per-file granularity.
  • Verifies that class names end with Test and match their filename exactly (FunctionUnderTest[OptionalSubsetIndicator]Test).
• Support File Exclusions: Automatically skips test helper/harness files (such as base.php), mock fixtures, and data directories.

Testing Instructions

1. Review workflow trigger configuration and permissions in .github/workflows/validate-phpunit-cleanup-pr.yml.
2. Open or update a pull request modifying test files under tests/phpunit/tests/ to trigger the Validate PHPUnit Test Cleanup Files workflow.
3. Verify that test files following the specification pass with success summaries, while non-compliant files or namespaces produce clear, actionable error logs.

AI Disclosure

• AI assistance: Yes
• Tool(s): JetBrains Junie
• Model(s): Gemini 2.5 Flash
• Used for: Developing the GitHub Actions workflow definition and JavaScript validation logic for test structure compliance.

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