How to test protected methods

a.php

    /**
     * Invoke protected or private method of object
     *
     * @param object $object
     * @param string $method name of method to invoke
     * @param mixed  $arg1   args that passed to invoked method [optional]
     *
     * @return mixed
     *
     * @throws \Exception
     */
    public static function callProtectedMethod($object, $method, $arg1 = null)
    {
        $args             = array_slice(func_get_args(), 2);
        $reflectionMethod = new \ReflectionMethod(get_class($object), $method);

        if ($reflectionMethod->isPublic()) {
            throw new \Exception(sprintf('%s::%s already accessible', get_class($object), $method));
        }

        $reflectionMethod->setAccessible(true);
        $result = $reflectionMethod->invokeArgs($object, $args);
        $reflectionMethod->setAccessible(false);

        return $result;
    }