symfony: PHPUnit tests almost 300% slower after Symfony update

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no
RFC?	no
Symfony version	3.3.10

Our project was running v3.2.6 and since it isn’t supported anymore we wanted to switch to Symfony 3.3. We created a new branch based on our master branch and made some changes to the code (removing deprecated stuff, etc.) but no major changes.

When running the tests of our project in the new branch it takes 15 minutes and 26 seconds whereas it only takes 6 minutes and 30 seconds in the master branch.

I found this issue: https://github.com/doctrine/annotations/pull/135#issuecomment-317174020 and we updated our dependency to doctrine/annotations from 1.4.0 to 1.5.0.

This already worked, it made our tests 5 minutes faster, so now it only takes 10 minutes and 50 seconds.

Type	Duration
master	6 minutes 30 seconds
update-branch	15 minutes 26 seconds
update-branch (updated annotations)	10 minutes 50 seconds

For all those tests I deleted the cache folders beforehand, did a composer install, etc. so I always have the same preconditions.

In the linked PR from doctrine/annotations @Ocramius said

as for the performance issue caused by multiple reset() or registerLoader() calls, that cannot be fixed without introducing BC breaks 😦

so is there nothing else that can be done to improve performance?

What we changed

• replaced kernel.root_dir with kernel.project_dir (same for the methods getRootDir() in AppKernel)
• removed trusted_proxies from config.yml and now calling it in the app.php and app_dev.php

But this alone shouldn’t be responsible for an execution time that is 4 minutes longer, right?