Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / vendor / phpunit / phpunit / tests / _files / ChangeCurrentWorkingDirectoryTest.php

<?php
class ChangeCurrentWorkingDirectoryTest extends PHPUnit_Framework_TestCase
{
    public function testSomethingThatChangesTheCwd()
    {
        chdir('../');
        $this->assertTrue(true);
    }
}