Shortcode to get featured image of specific id post

Using your example I’ve updated it to return instead of the title the image.

function post_shortcode( $atts ) {
    extract(
        shortcode_atts(
            array(
                'id' => '',
            ),
            $atts
        )
    );

    if ( isset( $id ) ) {
        return '<a href="' . get_permalink( $id ) . '">' . get_the_post_thumbnail( $id, 'thumbnail' ) . '</a>';
    }
}

add_shortcode( 'test', 'post_shortcode' );