public static function assertInstanceOf(string $className, $actual, string $message = '')
    {
        self::$count += 1;

        if ($actual instanceof $className) {
            return;
        }

        if (!$message) {
            $message = sprintf(
                'Failed asserting that %s is an instance of %s',
                static::getType($actual),
                $className
            );
        }
        throw new AssertionError($message);
    }