Testing against the filesystem with vfsStream

Code
<?php

use org\bovigo\vfs\vfsStream;
use 
PHPUnit\Framework\TestCase;

class 
FsTest extends TestCase
{
    public function 
testFileExists() : void
    
{
        
/* @var $baseDir org\bovigo\vfs\vfsStreamDirectory */
        
$baseDir vfsStream::setup('dir');
        
        
mkdir(vfsStream::url('dir')  . '/' 'myDir');
        
        
$this->assertTrue($baseDir->hasChild('myDir'));
        
$this->assertTrue(file_exists(vfsStream::url('dir')  . '/' 'myDir'));
    }
}
Result
Time: 287 ms, Memory: 14.00 MB

OK (1 test, 0 assertions)
Used Versions
PHP 7.3, Zend 3.0, Symfony 4.3, Laravel 5.8, PHPUnit 8.0, Doctrine 2.10