CrawlerTest.php

<?php

use Symfony\Component\DomCrawler\Crawler;

class CrawlerTest extends \PHPUnit_Framework_TestCase
{
    public function testAttribute()
    {
        $xml = <<<XML
<div>
    <a>Foo</a>
    <a rel="somefield[withKey]">Bar</a>
    <a rel="somefield[withKey]" href="http://example.com">Baz</a>
</div>
XML;


        $crawler = new Crawler($xml);
        $this->assertEquals([
            '',
            'http://example.com',
        ], $crawler->filterXPath('//a[@rel="somefield[withKey]"]')->extract(['href']));

        $this->assertEquals([
            'http://example.com',
        ], $crawler->filterXPath('//a[@rel="somefield[withKey]"][@href]')->extract(['href']));
    }
}