OK…progress. Lots of error messages, but followed thru and restarted DW. Recreated cart on tester. All worked. Uploaded, not only using DW, which sometimes doesn't get everything up, but also Transmit. Checked to see if all files were on server. All good.
Went to test shopping page, all good. Passed to cart.php. All good. Update quantity all good.
Check out went to a blank checkout.php page.