As with any code, you should test your objectives. When you wrote your nice httpd what did you set out to achieve? Test these things.
You should test the features that your httpd provides, as well as those aspects of the HTTP specification that you claim to support. Ideally, you would also test how your httpd responds to requests it can't deal with. The HTTP Implementor's Forum might help you.
LWP::Simple will allow you to perform simple tests (as its name suggests!), but you won't be able to use HTTP's POST method. I would suggest you investigate Test::WWW::Mechanize.
Finally, you might want to test your httpd against the behaviour of common browsers using Win32::IE::Mechanize or the WWW::Mechanize::Shell modules.