The Symfony project uses a third-party service which automatically runs tests for any submitted patch. If the new code breaks any test, the pull request will show an error message with a link to the full error details.
In any case, it's a good practice to run tests locally before submitting a patch for inclusion, to check that you have not broken anything.
To run the Symfony test suite, install the external dependencies used during the tests, such as Doctrine, Twig and Monolog. To do so, install Composer and execute the following:
$ composer update
Then, run the test suite from the Symfony root directory with the following command:
$ php ./phpunit symfony
The output should display
OK. If not, read the reported errors to figure out
what's going on and if the tests are broken because of the new code.
The entire Symfony suite can take up to several minutes to complete. If you
want to test a single component, type its path after the
$ php ./phpunit src/Symfony/Component/Finder/