8.x-1.x branch fails testing with PHPUnit 9 due to expectExceptionMessageRegExp()

Actually, for max compatibility, a little bit of tech debt in this test (on an EOL branch) lets this test pass on basically all versions of core with any version of PHPUnit. You probably don't care about pre-PHPUnit 8 support in 2.0.x and higher, so we can leave commit d265fcee69a alone over there.

Thoughts?

Thanks!
-Derek

The test makes all tests green again.

Reviewed the code, and it is exactly what symfony does in phpunit-bridge (\Symfony\Bridge\PhpUnit\Legacy\PolyfillTestCaseTrait).
So if there were (or are to come) more PHPUnit compatibility breaks, i'd recommend using https://symfony.com/doc/current/components/phpunit_bridge.html, but for this single instance this is good and pragmatic.

See 📌 Initiative for Group 1.x compatibility under Drupal 10 Fixed

I don't think a compatibility mode is still necessary due to the minimum Drupal version being 9.5 or 10 now.