Wrap Custom HTML WordPress blocks in a div wrapper

functions.php

<?php

add_filter( 'render_block', 'custom_wrap_html_block_output', 10, 2 );
/**
 * Wrap output of HTML blocks.
 *
 * @param string $block_content Original block content.
 * @param array $block Block info.
 * @return string The block content with a wrapper.
 */
function custom_wrap_html_block_output( $block_content, $block ) {
	if ( 'core/html' === $block['blockName'] ) {
		$block_content = '<div class="test">' . $block_content . '</div>';
	}

	return $block_content;
}