Snippet for adding a basic Publishing Checklist

publishing-checklist-integration.php

<?php

	add_action( 'publishing_checklist_init', function() {
	$args = array(
		'label'           => esc_html__( 'Featured Image', 'demo_publishing_checklist' ),
		'callback'        => function ( $post_id, $id ) {
			return has_post_thumbnail( $post_id );
		},
		'explanation'     => esc_html__( 'A featured image is required.', 'demo_publishing_checklist' ),
		'post_type'       => array( 'post' ),
	);
	Publishing_Checklist()->register_task( 'demo-featured-image', $args );
} );