Integrationtests in PHPUnit with mock proxies

Code
<?php

use Symfony\Component\Yaml\Parser;
use PHPUnit\Framework\TestCase;

class MockProxyTest extends TestCase
{
    public function testParseStr() : void
    {
        $str = 'root: ' . PHP_EOL .
            '  key1: value1' . PHP_EOL .
            '  key2: value2';
        
        $parser = $this->getMockBuilder(Parser::CLASS)
            ->enableProxyingToOriginalMethods()
            ->getMock();
        $parser->expects($this->once())
            ->method('parse');
        
        $val = (new Foo($parser))->parseStr($str);
        
        $this->assertEquals('value1', $val['root']['key1']);
        $this->assertEquals('value2', $val['root']['key2']);
    }
}

class Foo
{
    private $parser;
    
    public function __construct(Parser $parser)
    {
        $this->parser = $parser;
    }
    
    public function parseStr($str)
    {
        return $this->parser->parse($str);
    }
}
Result
Time: 00:00.010, Memory: 18.00 MB

OK (1 test, 0 assertions)
Used Versions
PHP 8.3, Laminas MVC 3.2, Symfony 5.2, Laravel 8.28, PHPUnit 9.5, Doctrine ORM 2.8