I like RS232MON from EVMSoft.com as a test tool.
Can select data format (hex,text/ascii, bin, dec, float)
on both Rx & Tx, and on Tx can send repeating a file, or bursts of characters, in 1mS and up periods.
I've been using it a lot to test out a Tx card that spits out RS232 at 115,200 to see if the correct stuff was coming out,
and sending that same data into an Rx card to see if it was reacting properly.