take a look at this
Apache::Test
its included in the modperl tarball as well as the bug report mechanisms...
...basically it starts up an apache process and can run and test mod_perl handlers,
as well as cgi-bin/ scripts via various .t's. check the examples

httpd.apache.org/test has other stuff i havent checked into in a while...

the other one ive spent some time with is HTTP::WebTest which works pretty good as well

there are others for testing various other things , such as seige for testing a server with different amounts of users... or the w3c html validator for linkages