CookieTest.php

<?php

protected function assertCookie($key, $value)
{
    $headers = new Collection($this->response->headers->allPreserveCase());
    $cookies = new Collection($headers->get('Set-Cookie', []));

    $matches = $cookies->filter(function($raw_cookie) use ($key, $value) {
        list($raw_value)            = explode('; ', $raw_cookie);
        list($set_name, $set_value) = explode('=', $raw_value);

        if ($set_name == $key && $set_value == $value) {
            return true;
        }
    });

    $this->assertCount(1, $matches, "Could not find cookie for '{$key}' / '{$value}'");

    return $this;
}