As described there by Alexandre Salomé, you might want to rollback the database changes executed during your tests.
But you'll get the following error, if you want to test a Doctrine event listener in a functional test:
Uncaught PHP Exception InvalidArgumentException: "Entity has to be managed or scheduled for removal for single computation Cheric\ExampleBundle\Entity\Article@00000000055581e0000000001ac20431" at /home/cherik/BlogIsolationTests/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php line 427
To fix this, you'll need to use the correct EventManager in your DBAL Connection when keeping the same connection between Symfony requests in your tests.