Store the values passed to a hook invocation.
$op: One of the hook_file_* operations: 'load', 'validate', 'download', 'insert', 'update', 'copy', 'move', 'delete'.
$args: Values passed to hook.
function _file_test_log_call($op, $args) {
$results = state()
->get('file_test.results') ?: array();
$results[$op][] = $args;
state()
->set('file_test.results', $results);
}