from symfony sources : Symfony\Bundle\FrameworkBundle\Test\WebTestCase

tests.php

    /**
     * Creates a Kernel.
     *
     * Available options:
     *
     *  * environment
     *  * debug
     *
     * @param array $options An array of options
     *
     * @return KernelInterface A KernelInterface instance
     */
    protected static function createKernel(array $options = array())
    {
        if (null === static::$class) {
            static::$class = static::getKernelClass();
        }

        return new static::$class(
            isset($options['environment']) ? $options['environment'] : 'test',
            isset($options['debug']) ? $options['debug'] : true
        );
    }

    /**
     * Creates a Kernel.
     *
     * Available options:
     *
     *  * environment
     *  * debug
     *
     * @param array $options An array of options
     *
     * @return KernelInterface A KernelInterface instance
     */
    protected static function createKernel(array $options = array())
    {
        if (null === static::$class) {
            static::$class = static::getKernelClass();
        }

        return new static::$class(
            isset($options['environment']) ? $options['environment'] : 'test',
            isset($options['debug']) ? $options['debug'] : true
        );
    }