WordPress Docx - apply_filters - Testing when no callbacks are registered.

apply_filters.php

add_filter( 'knowthecode', function( $value ){
	d( 'in the filter knowthecode ' . $value );
}, 52 );

add_action( 'loop_start', __NAMESPACE__ . '\demo_no_callbacks' );
function demo_no_callbacks() {
	echo 'in demo_no_callbacks<br>';

	global $wp_filter;

	d( $wp_filter['knowthecode'] );

	remove_all_filters( 'knowthecode' );

	d( $wp_filter['knowthecode'] );

	d( array_key_exists( 'knowthecode', $wp_filter ) );

	$value = apply_filters( 'knowthecode', 'Hello there' );

	echo 'back from apply_filters';
	d( $value );
}