Actually the last thing is quite a good one, may be archaic but I do it quite often while testing code for work. just run your code on the command line like this :

bash$>./perlmonksrule.pl "paramname=paramvalue&paramname2=paramvalue2"
[download]

You are basically passing the code's STDIN exactly what apache sees and then inturn passes to your STDIN to be parsed my your CGI.pm.