This changeset updates the test suite to declare and validate helper variables (for future PHP 8.2+ compatibility and because these variables may report an E_DEPRECATED in tests for PHP 8.1+). This only affects the test suite and is a bit harder to reproduce in this repository itself, but I've stumbled over this while updating ReactPHP's combined test suite that runs all tests of all components and happens to report said E_DEPRECATED on PHP 8.1+.

I'll link the downstream PR against this one, a failed test run reported a bunch of these messages:

Deprecated: file_exists(): Passing null to parameter #1 ($filename) of type string is deprecated in /data/vendor/react/event-loop/tests/ExtLibeventLoopTest.php on line 29