Implements callback_batch_operation().
Simple batch operation.
function _batch_test_callback_1($id, $sleep, &$context) {
// No-op, but ensure the batch take a couple iterations.
// Batch needs time to run for the test, so sleep a bit.
usleep($sleep);
// Track execution, and store some result for post-processing in the
// 'finished' callback.
batch_test_stack("op 1 id {$id}");
$context['results'][1][] = $id;
}