PHP Fatal error:  Cannot make static method PHPUnit_Framework_Assert::assertFileExists() non static in class Drupal\Tests\file\Functional\FileFieldTestBase in /Users/USER/Documents/workspace/drupal/core/modules/file/tests/src/Functional/FileFieldTestBase.php on line 302
PHP Stack trace:
PHP   1. {main}() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/phpunit:0
PHP   2. PHPUnit_TextUI_Command::main() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/phpunit:47
PHP   3. PHPUnit_TextUI_Command->run() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/TextUI/Command.php:100
PHP   4. PHPUnit_TextUI_Command->handleArguments() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/TextUI/Command.php:110
PHP   5. PHPUnit_Util_Configuration->getTestSuiteConfiguration() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/TextUI/Command.php:636
PHP   6. PHPUnit_Util_Configuration->getTestSuite() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/Util/Configuration.php:868
PHP   7. PHPUnit_Framework_TestSuite->addTestFile() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/Util/Configuration.php:988
PHP   8. ReflectionMethod->invoke() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/Framework/TestSuite.php:374
PHP   9. Drupal\Tests\TestSuites\FunctionalTestSuite::suite() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/Framework/TestSuite.php:374
PHP  10. Drupal\Tests\TestSuites\TestSuiteBase->addTestsBySuiteNamespace() /Users/USER/Documents/workspace/drupal/core/tests/TestSuites/FunctionalTestSuite.php:22
PHP  11. PHPUnit_Framework_TestSuite->addTestFiles() /Users/USER/Documents/workspace/drupal/core/tests/TestSuites/TestSuiteBase.php:55
PHP  12. PHPUnit_Framework_TestSuite->addTestFile() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/Framework/TestSuite.php:403
PHP  13. PHPUnit_Util_Fileloader::checkAndLoad() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/Framework/TestSuite.php:331
PHP  14. PHPUnit_Util_Fileloader::load() /Users/USER/Documents/workspace/drupal/vendor/phpunit/phpunit/src/Util/Fileloader.php:36