How to see if the test works? There is a way to see if the Drupal tests are working? I wanted to test the FileSystemTest, but when I type phpunit command on the test folder this error appears: 

1) Drupal\Tests\Core\File\FileSystemTest::testChmodFile
Argument 1 passed to Drupal\Core\File\FileSystem::__construct() must be an instance of Drupal\Core\File\StreamWrapperManagerInterface, instance of Mock_StreamWrapperManagerInterface_428d696c given, called in /var/www/html/drupal-8.0.5/core/lib/tests/FileSystemTest.php on line 43 and defined

/var/www/html/drupal-8.0.5/core/lib/Drupal/Core/File/FileSystem.php:62
/var/www/html/drupal-8.0.5/core/lib/tests/FileSystemTest.php:43
/home/bianca/.composer/vendor/phpunit/phpunit/src/TextUI/Command.php:153
/home/bianca/.composer/vendor/phpunit/phpunit/src/TextUI/Command.php:105


Someone know how to make the test work with phpunit?
See https://www.drupal.org/node/2116263.

You either need to run it inside the core folder, or (easier IMHO), you need to pass the -c core argument, so it finds the phpunit documentation.

Also note that only a part of Drupal's tests are phpunit, others are based on our own test framework and you need to run them with run-tests.sh or through the UI.

That said, you only need to run core tests if you work patches for Drupal core. Drupal's tests always path, nothing is added unless it is passing all tests.