I did not merge your changes from #39736 into 5.x because I didn't know how to resolve merge conflicts.

Could you please update this PR to include the relevant changes that should be borrowed from 5.2?

Sure 👍

Looks ok now, don't know why two bridges have:

Fatal error: Uncaught Error: Class 'Symfony\Component\Notifier\Tests\TransportFactoryTestCase' not found in /home/travis/build/symfony/symfony/src/Symfony/Component/Notifier/Bridge/Discord/Tests/DiscordTransportFactoryTest.php:18

Fatal error: Uncaught Error: Class 'Symfony\Component\Notifier\Tests\TransportFactoryTestCase' not found in /home/travis/build/symfony/symfony/src/Symfony/Component/Notifier/Bridge/Esendex/Tests/EsendexTransportFactoryTest.php:18

but not the other 🤔

cc @derrabus @nicolas-grekas

Didn't we want to move those abstract test classes out of the Tests folder anyway on 5.x?

Let's do it a little bit later because IIRC some open PRs for new bridges use it like this, and I want to get them merged before, otherwise it's a never ending story for them to get in 😑

Those failures look like composer hickups to me: Composer could not fetch from git so it fell back to fetching the ZIP. I've rebased the PR to verify my hypothesis.

Thank you Oskar.

Thanks for the feedback ✌🏻