PHP: $this is not available in non object context : I have a class with the following structure:

    /**
     * @property int ticket_id
     */
    class Test {
    	public function __construct( $ticket_id ) {
    		$this->ticket_id = $ticket_id;
    
    		$this->register();
    	}
    
    	/**
    	 * Register all hooks
    	 */
    	public function register(): void {
    		add_action( 'wp_ajax_test', array( $this, 'test' ) );
    	}
    
    	public function test(): void {
    		require_once('test.php');
    	}
    }

In my `test.php` I've tried using my parameter `$this->ticket_id` but I got an error that `$this` is not available in non object context. Why? I thought I can use it inside any required file too.