Per issue https://www.drupal.org/project/drupal/issues/3589108 And change record https://www.drupal.org/node/3594014 `SYMFONY_DEPRECATIONS_HELPER` will be ignored in favour of the `phpunit.xml.dist` configuration file changes. We take core's one if none is present, so that part is fine. I think we need to update the description and docs. **Tasks** - [ ] Update variable description to mention it is deprecated. - [ ] Update docs mentioning it is deprecated. - [ ] Consider using `--suppress-deprecations` by default when running `run-tests.sh`. > Related to: https://www.drupal.org/project/drupal/issues/3589108