TEST_RECIPIENT_OVERRIDE
Send a small number of emails from this batch to one address of your choice, instead of the real customer emails. No real customers receive anything from a test run.
Test mode also caps how many rows of the batch are processed, so even on a 10,000-row batch you'll only generate the chosen number of PDFs + emails.
Preview hits SQL Server with the same filters as the real run, returns a count, and lets you confirm before kicking anything off.