Integrate with PHPUnit

[beberlei]

The VerifyDeprecations trait exists to add assertions about deprecations which is a deprecation-producer task. For deprecation consumers we still need to check how to integrate with PHPUnit.

[Jean85]

You can probably do it with PHPUnit 10 and its new event system. BTW that is already wired to an error handler, so triggering those would automatically work out of the box.