enable to create a short code

Hello
I’m using a child theme, and in the function.php of the child theme, I wrote a function to insert a inline image in my text :

add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );
function theme_enqueue_styles() {
    wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );
}
//create short code to insert molecule.png
function molecule_link_shortcode() {
return '<img src="https://test.mysite.fr/wp-content/uploads/2017/02/molecule.png" alt="" style="border: 0px"/>';
}
add_shortcode('molecule', 'molecule_link_shortcode');

but in my article, the shortcode [molecule] has no effect
any advice?

Rgds

xavier