Take screenshot with Behat/Mink after failed step

gistfile1.aw

/**
 * Take screenshot when step fails.
 * Works only with Selenium2Driver.
 * 
 * @AfterStep
 */
public function takeScreenshotAfterFailedStep($event)
{
    if (4 === $event->getResult()) {
        $driver = $this->getSession()->getDriver();
        if (!($driver instanceof Selenium2Driver)) {
            //throw new UnsupportedDriverActionException('Taking screenshots is not supported by %s, use Selenium2Driver instead.', $driver);
            return;
        }

        $screenshot = $driver->wdSession->screenshot();
        file_put_contents('/tmp/test.png', base64_decode($screenshot));
    }
}

Another dedicated extension with support for Mink (Goutte) and Selenium screenshots
https://github.com/integratedexperts/behat-screenshot

Another extension that gives more than just a screenshot with minimal setup! https://github.com/forceedge01/behat-fail-aid