phpunit breaks symfony autoloader?

[sc0rp10]

Hi!
Today I was updated my symfony projects to 3.2 version which contains some changes in Yaml component: It's now can handle PHP constants in code and class Symfony\Component\Yaml\Yaml have new constant PARSE_CONSTANT.
When I ran tests with globally installed phpunit I got error Error: Undefined class constant 'PARSE_CONSTANT' in /tmp/test/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php:396
I add some debug to this line:

if (!defined(Yaml::class.'PARSE_CONSTANT')) {
    $rc = new \ReflectionClass(Yaml::class);
    var_dump($rc->getFileName());
}

And got string phar:///usr/local/Cellar/phpunit/5.6.2/libexec/phpunit-5.6.2.phar/symfony/yaml/Yaml.php what means that class Symfony\Component\Yaml\Yaml was loaded from phpunit's phar, and not from my vendor directory.

I've tried to reproduce this with clean symfony's 3.2 installation with default phpunit.xml and got same error.

I created repository with clean symfony 3.2 and this bug: https://github.com/sc0rp10/phpunit-symfony-issue
Clone it, install vendors and run globally installed phpunit (my version is 5.6.2).

Is it PHPUnit issue or symfony?

[sebastianbergmann]

Duplicate of #2015. In the meantime install PHPUnit via Composer.