Screenshots on Behat failed steps

behat.yml

default:
    context:
        class: Acme\Behat\Context\MyContext
        parameters:
            screenshots_path: web/tmp # don't forget to create and make writable this directory!

MyContext.php

<?php

namespace Acme\Behat\Context;

use Behat\Behat\Context\BehatContext;
use Behat\MinkExtension\Context\MinkContext;
use Behat\Behat\Event\StepEvent;

class MyContext extends BehatContext
{
    /**
     * @var array
     */
    protected $parameters;

    /*
        Behat pass parameters as an array to context constructor
    */
    public function __construct(array $parameters)
    {
        $this->parameters = $parameters;
    }
    
    /**
     * Take a screenshot when a (any) step fails.
     * Works only with Selenium.
     * @AfterStep
     */
    public function takeScreenshotOnFailure(StepEvent $event)
    {
        if ($event->getResult() == StepEvent::FAILED) {
            $path = $this->parameters['screenshots_path'];
            $imageData = $this->getMink()->getSession()->getDriver()->getScreenshot();

            $scenarioName = str_replace(' ', '_', $event->getStep()->getParent()->getTitle());
            $filename = sprintf('fail_%s_%s.png', time(), $scenarioName);

            file_put_contents(rtrim($path, '/').'/'. $filename, $imageData);
        }
    }

    /**
     * @return MinkContext
     * @throws \RuntimeException
     */
    protected function getMink()
    {
        $mink = $this->getMainContext()->getSubcontext('mink');

        if (!$mink instanceof MinkContext) {
            throw new \RuntimeException(sprintf('Expected a "MinkContext", got a "%s".', is_object($mink) ? get_class($mink) : gettype($mink)));
        }

        return $mink;
    }
}