app/config/security_test.php

<?php

$this->import('security.php');

// Support HTTP basic auth for test logins
$container->loadFromExtension('security',
    [
        'firewalls' => [
            'main' => [
                // Support HTTP basic auth for test logins
                'http_basic' => true,
            ],
        ],
        'encoders'  => [
            'Symfony\Component\Security\Core\User\User' => [
                'algorithm'        => 'md5',
                'encode_as_base64' => false,
                'iterations'       => 0,
            ],
            'Mautic\UserBundle\Entity\User' => [
                'algorithm'        => 'md5',
                'encode_as_base64' => false,
                'iterations'       => 0,
            ],
        ],
    ]
);