If you want to do this reliably, don't use the GMail auto-forward stuff. Instead, create yourself a _filter_ with the following definition:

Matches: -{"X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*"} Do this: Skip Inbox, Forward to XXX, Delete it

Your other GMail account will take care of the spam that gets forwarded.

I've been doing this for more than a year, with nothing ending up in the account's Spam folder.