Core Ticket 51423: test script to make `wp_json_encode` fail during generation of personal data export JSON file.

51423.php

<?php
namespace Testing\Ticket51423;

add_action( 'wp_privacy_personal_data_export_file', __NAMESPACE__ . '\setup_testing_export_file', 5 );
function setup_testing_export_file( $request_id ) {
	$GLOBALS['testing_51423'] = array(
		'request_id'           => $request_id,
		'_export_data_grouped' => get_post_meta( $request_id, '_export_data_grouped', true ),
	);

	add_filter( 'get_post_metadata', __NAMESPACE__ . '\filter_export_data_grouped', 99, 3 );
}

function filter_export_data_grouped( $value, $id, $meta_key ) {
	if ( '_export_data_grouped' !== $meta_key ) {
		return $value;
	}

	if ( $GLOBALS['testing_51423']['request_id'] !== $id ) {
		return $value;
	}

	// Taken from the function.
	$exports_dir          = wp_privacy_exports_dir();
	$obscura              = wp_generate_password( 32, false, false );
	$json_report_filename = "wp-personal-data-file-{$obscura}.json";
	$json_report_pathname = wp_normalize_path( $exports_dir . $json_report_filename );
	$file                 = fopen( $json_report_pathname, 'w' );

	// Add the resource to the meta which should make the encoding fail.
	$value                     = $GLOBALS['testing_51423']['_export_data_grouped'];
	$value['user']['resource'] = $file;

	return array( $value );
}