Get the arguments passed to invocation of a given hook since file_test_reset() was last called.
$op: One of the hook_file_* operations: 'load', 'validate', 'download', 'insert', 'update', 'copy', 'move', 'delete'.
Array of the parameters passed to each call.
function file_test_get_calls($op) {
$results = state()
->get('file_test.results') ?: array();
return $results[$op];
}